Generate transfer codings with chunked first and last in the HTTP/1 fuzz

[ericmj]

Responses with more than one transfer coding could come up, as a generated Transfer-Encoding: chunked plus a random Transfer-Encoding: gzip header, but no invariant compared the body size Mint delivered with what the framing gives, so treating the first coding as the framing one went unnoticed. Chunked bodies are now also sent with "gzip, chunked", which RFC 9112 section 6.3 frames as chunked, and with "chunked, gzip", whose body is read until the connection closes and includes the chunk framing.

Each generated framing carries the body length it gives, and the model checks the body size of completed responses to the initial requests. That holds when the bytes are unmutated, every initial request was issued, and the response and the ones before it are 1.1 responses to GET or POST with a 200, 404 or 500 status, no 101, and no extra framing headers. Responses to requests issued mid-scenario aren't checked. A response read until close takes the rest of the bytes, so no response after it has a known size.

[coveralls]

Coverage Report for CI Build 5

Coverage decreased (-0.05%) to 90.457%

Details

• Coverage decreased (-0.05%) from the base build.
• Patch coverage: No coverable lines changed in this PR.
• 2 coverage regressions across 1 file.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

2 previously-covered lines in 1 file lost coverage.

File	Lines Losing Coverage	Coverage
lib/mint/http2.ex	2	95.28%

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Coverage Stats

Relevant Lines:	1970
Covered Lines:	1782
Line Coverage:	90.46%
Coverage Strength:	718.29 hits per line

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💛 - Coveralls