Fix type instability in convs using CompoundPeriod (JuliaLang#54995)

The functions `toms`, `tons`, and `days` uses `sum` over a vector of
`Period`s to obtain the conversion of a `CompoundPeriod`. However, the
compiler cannot infer the return type because those functions can return
either `Int` or `Float` depending on the type of the `Period`. This PR
forces the result of those functions to be `Float64`, fixing the type
stability.

Before this PR we had:

```julia
julia> using Dates

julia> p = Dates.Second(1) + Dates.Minute(1) + Dates.Year(1)
1 year, 1 minute, 1 second

julia> @code_warntype Dates.tons(p)
MethodInstance for Dates.tons(::Dates.CompoundPeriod)
  from tons(c::Dates.CompoundPeriod) @ Dates ~/.julia/juliaup/julia-nightly/share/julia/stdlib/v1.12/Dates/src/periods.jl:458
Arguments
  #self#::Core.Const(Dates.tons)
  c::Dates.CompoundPeriod
Body::Any
1 ─ %1  = Dates.isempty::Core.Const(isempty)
│   %2  = Base.getproperty(c, :periods)::Vector{Period}
│   %3  = (%1)(%2)::Bool
└──       goto mmtk#3 if not %3
2 ─       return 0.0
3 ─ %6  = Dates.Float64::Core.Const(Float64)
│   %7  = Dates.sum::Core.Const(sum)
│   %8  = Dates.tons::Core.Const(Dates.tons)
│   %9  = Base.getproperty(c, :periods)::Vector{Period}
│   %10 = (%7)(%8, %9)::Any
│   %11 = (%6)(%10)::Any
└──       return %11


julia> @code_warntype Dates.toms(p)
MethodInstance for Dates.toms(::Dates.CompoundPeriod)
  from toms(c::Dates.CompoundPeriod) @ Dates ~/.julia/juliaup/julia-nightly/share/julia/stdlib/v1.12/Dates/src/periods.jl:454
Arguments
  #self#::Core.Const(Dates.toms)
  c::Dates.CompoundPeriod
Body::Any
1 ─ %1  = Dates.isempty::Core.Const(isempty)
│   %2  = Base.getproperty(c, :periods)::Vector{Period}
│   %3  = (%1)(%2)::Bool
└──       goto mmtk#3 if not %3
2 ─       return 0.0
3 ─ %6  = Dates.Float64::Core.Const(Float64)
│   %7  = Dates.sum::Core.Const(sum)
│   %8  = Dates.toms::Core.Const(Dates.toms)
│   %9  = Base.getproperty(c, :periods)::Vector{Period}
│   %10 = (%7)(%8, %9)::Any
│   %11 = (%6)(%10)::Any
└──       return %11


julia> @code_warntype Dates.days(p)
MethodInstance for Dates.days(::Dates.CompoundPeriod)
  from days(c::Dates.CompoundPeriod) @ Dates ~/.julia/juliaup/julia-nightly/share/julia/stdlib/v1.12/Dates/src/periods.jl:468
Arguments
  #self#::Core.Const(Dates.days)
  c::Dates.CompoundPeriod
Body::Any
1 ─ %1  = Dates.isempty::Core.Const(isempty)
│   %2  = Base.getproperty(c, :periods)::Vector{Period}
│   %3  = (%1)(%2)::Bool
└──       goto mmtk#3 if not %3
2 ─       return 0.0
3 ─ %6  = Dates.Float64::Core.Const(Float64)
│   %7  = Dates.sum::Core.Const(sum)
│   %8  = Dates.days::Core.Const(Dates.days)
│   %9  = Base.getproperty(c, :periods)::Vector{Period}
│   %10 = (%7)(%8, %9)::Any
│   %11 = (%6)(%10)::Any
└──       return %11
```

After this PR we have:

```julia
julia> using Dates

julia> p = Dates.Second(1) + Dates.Minute(1) + Dates.Year(1)
1 year, 1 minute, 1 second

julia> @code_warntype Dates.tons(p)
MethodInstance for Dates.tons(::Dates.CompoundPeriod)
  from tons(c::Dates.CompoundPeriod) @ Dates ~/.julia/juliaup/julia-nightly/share/julia/stdlib/v1.12/Dates/src/periods.jl:458
Arguments
  #self#::Core.Const(Dates.tons)
  c::Dates.CompoundPeriod
Body::Float64
1 ─ %1  = Dates.isempty::Core.Const(isempty)
│   %2  = Base.getproperty(c, :periods)::Vector{Period}
│   %3  = (%1)(%2)::Bool
└──       goto mmtk#3 if not %3
2 ─       return 0.0
3 ─ %6  = Dates.Float64::Core.Const(Float64)
│   %7  = Dates.sum::Core.Const(sum)
│   %8  = Dates.tons::Core.Const(Dates.tons)
│   %9  = Base.getproperty(c, :periods)::Vector{Period}
│   %10 = (%7)(%8, %9)::Any
│   %11 = (%6)(%10)::Any
│   %12 = Dates.Float64::Core.Const(Float64)
│   %13 = Core.typeassert(%11, %12)::Float64
└──       return %13


julia> @code_warntype Dates.toms(p)
MethodInstance for Dates.toms(::Dates.CompoundPeriod)
  from toms(c::Dates.CompoundPeriod) @ Dates ~/.julia/juliaup/julia-nightly/share/julia/stdlib/v1.12/Dates/src/periods.jl:454
Arguments
  #self#::Core.Const(Dates.toms)
  c::Dates.CompoundPeriod
Body::Float64
1 ─ %1  = Dates.isempty::Core.Const(isempty)
│   %2  = Base.getproperty(c, :periods)::Vector{Period}
│   %3  = (%1)(%2)::Bool
└──       goto mmtk#3 if not %3
2 ─       return 0.0
3 ─ %6  = Dates.Float64::Core.Const(Float64)
│   %7  = Dates.sum::Core.Const(sum)
│   %8  = Dates.toms::Core.Const(Dates.toms)
│   %9  = Base.getproperty(c, :periods)::Vector{Period}
│   %10 = (%7)(%8, %9)::Any
│   %11 = (%6)(%10)::Any
│   %12 = Dates.Float64::Core.Const(Float64)
│   %13 = Core.typeassert(%11, %12)::Float64
└──       return %13


julia> @code_warntype Dates.days(p)
MethodInstance for Dates.days(::Dates.CompoundPeriod)
  from days(c::Dates.CompoundPeriod) @ Dates ~/.julia/juliaup/julia-nightly/share/julia/stdlib/v1.12/Dates/src/periods.jl:468
Arguments
  #self#::Core.Const(Dates.days)
  c::Dates.CompoundPeriod
Body::Float64
1 ─ %1  = Dates.isempty::Core.Const(isempty)
│   %2  = Base.getproperty(c, :periods)::Vector{Period}
│   %3  = (%1)(%2)::Bool
└──       goto mmtk#3 if not %3
2 ─       return 0.0
3 ─ %6  = Dates.Float64::Core.Const(Float64)
│   %7  = Dates.sum::Core.Const(sum)
│   %8  = Dates.days::Core.Const(Dates.days)
│   %9  = Base.getproperty(c, :periods)::Vector{Period}
│   %10 = (%7)(%8, %9)::Any
│   %11 = (%6)(%10)::Any
│   %12 = Dates.Float64::Core.Const(Float64)
│   %13 = Core.typeassert(%11, %12)::Float64
└──       return %13
```

Author: ronisbr

stdlib/Dates/src/periods.jl

@@ -451,11 +451,11 @@ toms(c::Second)      = 1000 * value(c)
 toms(c::Minute)      = 60000 * value(c)
 toms(c::Hour)        = 3600000 * value(c)
 toms(c::Period)      = 86400000 * days(c)
-toms(c::CompoundPeriod) = isempty(c.periods) ? 0.0 : Float64(sum(toms, c.periods))
+toms(c::CompoundPeriod) = isempty(c.periods) ? 0.0 : sum(p -> convert(Float64, toms(p))::Float64, c.periods)
 tons(x)              = toms(x) * 1000000
 tons(x::Microsecond) = value(x) * 1000
 tons(x::Nanosecond)  = value(x)
-tons(c::CompoundPeriod) = isempty(c.periods) ? 0.0 : Float64(sum(tons, c.periods))
+tons(c::CompoundPeriod) = isempty(c.periods) ? 0.0 : sum(p -> convert(Float64, tons(p))::Float64, c.periods)
 days(c::Millisecond) = div(value(c), 86400000)
 days(c::Second)      = div(value(c), 86400)
 days(c::Minute)      = div(value(c), 1440)
@@ -465,7 +465,7 @@ days(c::Week)        = 7 * value(c)
 days(c::Year)        = 365.2425 * value(c)
 days(c::Quarter)     = 91.310625 * value(c)
 days(c::Month)       = 30.436875 * value(c)
-days(c::CompoundPeriod) = isempty(c.periods) ? 0.0 : Float64(sum(days, c.periods))
+days(c::CompoundPeriod) = isempty(c.periods) ? 0.0 : sum(p -> convert(Float64, days(p))::Float64, c.periods)
 seconds(x::Nanosecond) = value(x) / 1000000000
 seconds(x::Microsecond) = value(x) / 1000000
 seconds(x::Millisecond) = value(x) / 1000