add gzip compression/decompression support

[Guest0x0]

This PR introduces gzip compression/decompression support for moonbitlang/async:

• an internal package moonbitlang/async/internal/gzip_internal provides state-machine style, IO-independent gzip encoding/decoding support
• a public package moonbitlang/async/gzip provides streaming gzip encoding/decoding support in the form of @io.Reader/@io.Writer transformer
• @http.Client can now automatically utilize HTTP gzip compression. It works as follows:
  • if the user explicitly supplied Accept-Encoding, automatic decompression will be skipped, the user get raw, encoded traffic when reading the response, and must manually decode the traffic
  • if the user did not supply Accept-Encoding, @http.Client will set Accept-Encoding: gzip,identity as a default. In this case, if the Content-Encoding is gzip from the server response, the client will perform automatic decompression, so the user still get uncompressed result, as intended
    • note that when automatic decompression happens, the Content-Length field will no longer be visible to the user (even if it is present) to avoid confusion, because it stores length of compressed content

[coveralls]

Coverage Report for CI Build 177

Coverage increased (+1.9%) to 78.405%

Details

• Coverage increased (+1.9%) from the base build.
• Patch coverage: 50 uncovered changes across 7 files (464 of 514 lines covered, 90.27%).
• No coverage regressions found.

Uncovered Changes

File	Changed	Covered	%
src/internal/gzip_internal/decoder.mbt	258	227	87.98%
src/http/parser.mbt	54	48	88.89%
src/internal/gzip_internal/encoder.mbt	99	94	94.95%
src/internal/gzip_internal/huffman.mbt	33	29	87.88%
src/internal/gzip_internal/metadata.mbt	20	18	90.0%
src/gzip/decoder.mbt	21	20	95.24%
src/gzip/encoder.mbt	15	14	93.33%

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	3825
Covered Lines:	2999
Line Coverage:	78.41%
Coverage Strength:	64785.94 hits per line

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💛 - Coveralls