fix: Fix header merging case-sensitivity issue

[fern-api]

Changes

This PR fixes a critical security issue with header merging:

Header Merging Security Fix (Fixes #1228)

• Fixed case-sensitivity issue in header merging that could lead to duplicate or ambiguous headers
• mergeHeaders and mergeOnlyDefinedHeaders now normalize header names to lowercase
• Prevents security issues where attackers could override SDK-provided headers (e.g., Authorization) by using different casing
• Ensures headers like Authorization and authorization are treated as the same header

Fern Auto-Generated Changes

• This PR includes auto-generated code updates from Fern to match the latest API Definition
• Updated form-urlencoded body serialization support
• Added comprehensive test coverage for complex nested objects and arrays in form data
• Dependency updates: @types/node, baseline-browser-mapping, caniuse-lite, graphql

References

• Fixes Small header merging issue #1228 - Small header merging issue (security vulnerability)

Testing

• This change adds unit test coverage
• This change adds integration test coverage

Checklist

• I have read the Auth0 general contribution guidelines
• I have read the Auth0 Code of Conduct
• All existing and new tests complete without errors

[codecov]

Codecov Report

❌ Patch coverage is 99.18256% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.94%. Comparing base (c98ea37) to head (f4cd203).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/management/core/headers.ts	66.66%	2 Missing ⚠️
...urces/jobs/resources/usersImports/client/Client.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1238      +/-   ##
==========================================
+ Coverage   79.56%   79.94%   +0.37%     
==========================================
  Files         515      515              
  Lines       18926    19287     +361     
  Branches     9056     9413     +357     
==========================================
+ Hits        15059    15419     +360     
- Misses       3867     3868       +1     

Flag	Coverage Δ
alltests	79.94% <99.18%> (+0.37%)	⬆️

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[developerkunal]

LGTM