fix(context): Allow Context.Value to properly support any key type

[kasidej]

Description

Fix an inconsistency in the Context.Value method where it accepted keys of any type in its signature but internally restricted them to strings when pass to Context.Get.

Motivation

The Context.Value method had a signature accepting any for keys, but its implementation only worked with string keys due to a type assertion when pass to Context.Get. This was inconsistent with Context.Set which properly support any comparable key type. I using custom types as context keys (a common Go pattern to avoid key collisions) would find that Value didn't work while Set did.

Changes

• modified Context.Value method in context.go
• add a test using a custom struct type in context_test.go

Pull Request Checklist

Please ensure your pull request meets the following requirements:

• Open your pull request against the master branch.
• All tests pass in available continuous integration systems (e.g., GitHub Actions).
• Tests are added or modified as needed to cover code changes.
• If the pull request introduces a new feature, the feature is documented in the docs/doc.md.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.99%. Comparing base (3dc1cd6) to head (b9d6964).
⚠️ Report is 230 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4492      +/-   ##
==========================================
- Coverage   99.21%   98.99%   -0.22%     
==========================================
  Files          42       44       +2     
  Lines        3182     2987     -195     
==========================================
- Hits         3157     2957     -200     
- Misses         17       21       +4     
- Partials        8        9       +1     

Flag	Coverage Δ
	?
--ldflags="-checklinkname=0" -tags sonic	98.98% <100.00%> (?)
-tags go_json	98.92% <100.00%> (?)
-tags nomsgpack	98.98% <100.00%> (?)
go-1.18	?
go-1.19	?
go-1.20	?
go-1.21	?
go-1.24	98.99% <100.00%> (?)
go-1.25	98.99% <100.00%> (?)
macos-latest	98.99% <100.00%> (-0.22%)	⬇️
ubuntu-latest	98.99% <100.00%> (-0.22%)	⬇️

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[Nurysso]

Looks good to me
@appleboy Can you please review it.