refactor(context): use http.StatusContinue constant instead of magic number 100

[mehrdadbn9]

Replace magic number `100` with `http.StatusContinue` constant for better code clarity and maintainability in `bodyAllowedForStatus` function.

Fixes #4489

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.27%. Comparing base (3dc1cd6) to head (7df2142).
⚠️ Report is 252 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4542      +/-   ##
==========================================
+ Coverage   99.21%   99.27%   +0.06%     
==========================================
  Files          42       46       +4     
  Lines        3182     3038     -144     
==========================================
- Hits         3157     3016     -141     
+ Misses         17       15       -2     
+ Partials        8        7       -1     

Flag	Coverage Δ
	?
--ldflags="-checklinkname=0" -tags sonic	99.27% <ø> (?)
-tags go_json	99.13% <ø> (?)
-tags nomsgpack	99.19% <ø> (?)
go-1.18	?
go-1.19	?
go-1.20	?
go-1.21	?
go-1.24	99.27% <ø> (?)
go-1.25	99.21% <ø> (?)
go-1.26	99.21% <ø> (?)
macos-latest	99.21% <ø> (-0.01%)	⬇️
ubuntu-latest	99.27% <ø> (+0.06%)	⬆️

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[Copilot]

Pull request overview

This pull request refactors the bodyAllowedForStatus function in context.go to replace the magic number 100 with the http.StatusContinue constant for better code clarity. Additionally, the PR includes extensive test coverage improvements across multiple files.

Changes:

• Replaced magic number 100 with http.StatusContinue constant in bodyAllowedForStatus function
• Added comprehensive test coverage for multiple functions across the codebase
• Added new test file for codec/json package

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
context.go	Replaced magic number 100 with http.StatusContinue constant and added clarifying comment
context_test.go	Added tests for http.StatusContinue, GetRawData with nil body, SameSiteDefaultMode cookie behavior, multipart form errors, and binding edge cases
utils_test.go	Added test for successful XML marshaling of H type
logger_test.go	Added test case for 400ms latency color
gin_test.go	Added tests for error handling in ServeHTTP
codec/json/json_test.go	New test file covering JSON codec API functions
binding/binding_test.go	Added test for Plain binding BindBody method

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