Fix WrapM pattern restore

[tigerwill90]

Restore req.Pattern on the original request in WrapM (the previous code reassigned req after req.WithContext, leaving the deferred restore pointing at the discarded clone), and expose http.Flusher to std-lib middleware via a small flusherWriter shim that delegates Flush() to FlushError() so middlewares like Coraza, gzip, or any stdlib code that type-asserts http.Flusher work correctly through WrapM.

[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 3 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
context.go	80.00%	2 Missing ⚠️
response_writer.go	50.00%	1 Missing ⚠️

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