Add unit tests for HTTP/1.1 parsing functions in docker_client.zig

[Copilot]

Description

Adds 22 unit tests covering the custom HTTP/1.1 client implementation in src/docker_client.zig. Tests use a pipeStream() helper that wraps a pre-filled POSIX pipe as std.net.Stream, enabling fully isolated testing without a real Docker socket.

HttpReader

• readByte: ordering, EndOfStream at EOF
• readExact: exact reads, EndOfStream on insufficient data
• readLine: CRLF/LF endings, null on empty EOF, partial data without newline, error.HttpHeaderTooLong on buffer overflow

parseResponseHead

• 200/404 status codes, Content-Length, chunked Transfer-Encoding
• Error cases: empty input, missing space, truncated status code
• Robustness: skips headers without :, case-insensitive names

readChunkedBody

• Single/multiple chunks, empty body, chunk extensions (;), optional trailers, invalid chunk size (returns accumulated data)

readUntilClose

• Full stream, empty stream, data pre-buffered in HttpReader.buf

sendHttpRequest

• GET request line and mandatory headers
• POST with Content-Type, Content-Length, and body appended

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring
• Performance improvement
• Test addition/modification
• CI/CD changes

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

Testing

• Unit tests

Tests run via zig build test --summary all. No Docker daemon required — all tests are pure unit tests using POSIX pipes as mock streams.

Additional Notes

The pipeStream() helper writes test data to a pipe's write end and closes it before returning the read end as a std.net.Stream. On both Linux and macOS, std.net.Stream.handle is i32, matching posix.fd_t, so pipe fds can be used directly.

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