Fix Accept-Encoding matching in compression middleware

[rupayon123]

Summary

Fix Accept-Encoding matching in compression middleware by comparing complete encoding tokens and respecting q=0. This prevents unsupported substring matches such as bgzip matching gzip and stops compression when a client explicitly marks an encoding unacceptable. Quality values outside the supported 0 < q <= 1 range are ignored as invalid.

Fixes #1069.

Validation

• Added table-driven cases for exact and case-insensitive tokens, whitespace, positive and zero quality values, invalid/out-of-range quality values, and substring false positives.
• Confirmed the regression tests fail against the original implementation.
• go test ./middleware -run '^TestMatchAcceptEncoding$' -count=1 passed.
• go test ./middleware -count=1 passed.
• go test ./... -count=1 passed.
• go vet ./... and git diff --check passed.

This change was prepared with AI assistance at the account holder's direction; the account holder is responsible for this submission and will handle any required project-specific process.