fix(s3): preserve equals in signed object paths

[jlon]

Type of Change

• New Feature
• Bug Fix
• Documentation
• Performance Improvement
• Test/CI
• Refactor
• Other: N/A

Related Issues

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

Summary of Changes

• vendor the pinned s3s dependency used by RustFS
• preserve = in SigV4 canonical object paths so signed GET requests do not fail signature verification for valid S3 object keys
• add an end-to-end regression test covering signed GET on a missing object whose key ends with =

Checklist

• I have read and followed the CONTRIBUTING.md guidelines
• Added/updated necessary tests
• Passed make pre-commit
• Documentation updated (if needed)
• CI/CD passed (if applicable)

Impact

• Breaking change (compatibility)
• Requires doc/config/deployment update
• Other impact: N/A

Additional Notes

Verification commands:

• cargo fmt --all --check
• cargo test -p e2e_test test_signed_get_nonexistent_object_with_trailing_equals_returns_nosuchkey -- --nocapture

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[github-actions]

CLA requirements are satisfied for this pull request.

[jlon]

Superseded by rustfs/s3s#10. The final RustFS-side PR will only bump the s3s revision and keep the regression test after the upstream fix is merged.