fix: preserve raw URI path for SigV4

[overtrue]

Summary

• Use the raw request URI path when building SigV4 canonical requests for header and presigned authentication.
• Keep decoded URI handling for S3 path parsing so bucket and object extraction behavior stays unchanged.
• Add regression coverage for signed requests whose raw URI path contains a trailing equals sign.

Related Issue

• S3 SignatureDoesNotMatch (403) instead of NoSuchKey (404) for non-existent objects with '=' in path rustfs#2477

Verification

• cargo test -p s3s v4_header_auth_uses_raw_uri_path_for_canonical_request -- --nocapture
• cargo test -p s3s sig_v4::methods --lib
• cargo test -p s3s ops::signature --lib
• cargo fmt --all --check

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Keep public canonical-request helpers in non-test builds

Adding #[cfg(test)] to this pub helper removes it from normal library builds, which is a breaking API change for any downstream code importing s3s::sig_v4::create_canonical_request (and similarly create_presigned_canonical_request). Because sig_v4 re-exports methods::*, callers that compiled before this commit will now fail with unresolved symbols outside tests.

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[overtrue]

Superseded by upstream PR s3s-project#570.