feat: add HTTP response compression middleware

[noneandundefined]

Summary

• add provider-based HTTP response compression middleware with Accept-Encoding quality negotiation
• include built-in gzip support in the standard libchttpx build through zlib
• enable compression only at runtime through cHTTPX_CompressionUse(server, &config)
• add configurable minimum size, compression level and MIME include/exclude policy
• skip responses that should not be transformed (range, already encoded, no-transform, binary/precompressed MIME, etc.)
• allow compression to be disabled per route or per response
• add provider API designed for future Brotli/Zstandard implementations
• add real HTTP gzip integration tests, provider failure coverage and gzip decompression verification
• add CPU-vs-bandwidth benchmark, example and EN/RU documentation
• add zlib to Linux packages, Docker, installers and Windows/Linux CI dependencies

Build and test

No separate compression build flag is required:

make libchttpx.so
make examples-compression
make test-compression
make benchmark-compression

Application code decides whether compression is enabled:

chttpx_compression_config_t compression = cHTTPX_CompressionDefault();
compression.min_size = 1024;
compression.level = 5;

cHTTPX_CompressionUse(server, &compression);

TLS remains independently optional:

make TLS=1 libchttpx.so

Closes #47