fix: negotiate encoding before compression checks

[pratik-desgn]

Fixes #305.

The compression paths currently negotiate Accept-Encoding inside the last operand of a short-circuiting noCompress expression. When x-no-compression or a non-compressible content type matches first, encoding remains undefined and a configured onUnsupportedEncoding handler is called even for a supported encoding.

This change negotiates the encoding before evaluating the skip conditions in both the global onSend hook and reply.compress() paths. It adds regression coverage for each path and verifies that the response is passed through without invoking the unsupported-encoding handler.

This supersedes the voluntarily closed draft #404 and is rebased on current main.

Validation:

• npm run lint
• npm test — 236 unit tests and 10 type assertions passed
• git diff --check
• npm run benchmark --if-present completed all measurements, but its unchanged 8 KiB streaming control varied by 25% and exceeded the 10% noise tolerance; the benchmark reports this as machine noise and recommends rerunning on an idle machine before drawing conclusions

Checklist

• run npm run test && npm run benchmark --if-present
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer’s Certificate of Origin and the Code of Conduct