go: add syntax for error handling to Neon Go

[olegbbtr]

After a recent announcement 1 by Go team, saying they won't proceed
with adding error handling syntax to Go, it is evident we have to
implement a solution downstream.

We already build Linux kernel with custom patches (see #1386, #1392), it
is logical that as a next step we should have our own fork of Go, called
Neon Go.

The first feature is a syntax to handle errors. It supports the
following syntax:

... := ... handle err {
...
}

Which is equivalent to:

..., err := ...
if err != nil {
...
}

Advantages:

1. Easy to read.
2. Easy to write (no need to look for the ! key).

Timeline to implement:
5 June - merge to main
6 June - deploy to staging
7 June - deploy to production

Also, disable parts of the CI, as it doesn't have good support for Neon Go (yet).

NOTE: this is, of course, a joke. I don't have any strong opinions about
error handling in Go.

[Copilot]

Pull Request Overview

This PR introduces a new downstream syntax for simplified error handling (handle err { ... }) across the Neon Go codebase and integrates desugaring/resugaring scripts into the build pipeline.

• Replaces explicit if err != nil blocks with the concise handle err { ... } sugar in many packages.
• Adds desugar/resugar Makefile targets and makes build depend on desugar to apply transformations before vetting and compilation.
• Updates CI‐relevant files and helper functions to use the new syntax uniformly.

Reviewed Changes

Copilot reviewed 50 out of 50 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
pkg/neonvm/controllers/vm_qmp_queries.go	Replaced QMP error checks with handle err blocks.
pkg/neonvm/controllers/vm_controller_cpu_scaling.go	Applied handle err sugar in CPU scaling logic.
pkg/neonvm/controllers/vm_controller.go	Sugar‐ized reconciler steps (IPAM, certs, pods).
pkg/neonvm/controllers/runner_cpu_limits.go	Simplified error handling in runner CPU limits.
pkg/neonvm/controllers/certs.go	Used handle err for cert decoding and generation.
pkg/api/vminfo.go	Sugar in VM info extraction functions.
pkg/agent/watch.go	Applied sugar in VM watcher event creation.
pkg/agent/scalingevents/reporter.go	Sugar in NewReporter initialization.
pkg/agent/scalingevents/clients.go	Used sugar in client‐creation helpers.
pkg/agent/runner.go	Replaced HTTP and dispatcher error checks.
pkg/agent/entrypoint.go	Sugar in startup (Run) error flows.
pkg/agent/dumpstate.go	Simplified listener and dump error handling.
pkg/agent/dispatcher.go	Sugar in dispatcher and websocket connector.
pkg/agent/core/testhelpers/clock.go	Applied sugar to clock initialization.
pkg/agent/core/state_test.go	Used sugar in test helper (duration parsing).
pkg/agent/core/metrics.go	Sugar in metrics parsing and label extraction.
pkg/agent/config.go	Simplified config file open error.
pkg/agent/billing/clients.go	Sugar in billing client setup.
pkg/agent/billing/billing.go	Used sugar in NewMetricsCollector.
Makefile	Added .PHONY targets for desugar/resugar and updated build dependency.

Comments suppressed due to low confidence (2)

Makefile:166

• [nitpick] Add a note in the README or contributor guide explaining how and when to run scripts/desugar.sh and scripts/resugar.sh, so new developers understand the error-handling workflow.

.PHONY: resugar

Makefile:158

• Consider updating the CI configuration (e.g., GitHub Actions or other pipelines) to invoke make desugar before builds, ensuring the error-sugar transformations are applied consistently in all environments.

build: desugar vet bin/vm-builder ## Build all neonvm binaries.

[mikhail-sakhnov]

NOTE: this is, of course, a joke. I don't have any strong opinions about
error handling in Go.

Should be first line of the PR 😆

[mikhail-sakhnov]

I didn't read, but looks good to me 🚀