Replace strip_prefix-based header matching (only matched exact case and
lowercase) with a proper case-insensitive helper that splits on the
first colon and compares the header name using eq_ignore_ascii_case.
Adds tests for all-caps header names (CONTENT-LENGTH, TRANSFER-ENCODING).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

High-level HTTP client in the net crate bringing together TCP, TLS 1.3,
DNS, URL parsing, and HTTP message handling:

- HttpClient with get(), post(), request() methods
- Scheme handling: http:// (plain TCP) and https:// (TLS)
- Connection pooling by (host, port, is_tls) with max idle time and
max connections per host
- Redirect following (301, 302, 307, 308) with configurable max
- Configurable connect and read timeouts
- Streaming response reader: header detection, Content-Length,
chunked Transfer-Encoding, and read-until-close strategies
- std::io::Read and Write trait impls for TcpConnection

30+ unit tests covering error types, configuration, connection pool,
URL path building, header parsing, body strategy selection, and
chunked terminator detection.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

HTTP/1.1 message parser (RFC 7230, 7231) for the net crate:
- Request serialization (GET, POST, HEAD, PUT, DELETE, OPTIONS, PATCH)
- Response parsing: status line, headers, body
- Headers collection with case-insensitive name lookup
- Content-Length body reading
- Chunked Transfer-Encoding decoding (RFC 7230 §4.1)
- Content-Type parsing with charset extraction
- Proper handling of 1xx/204/304 no-body responses

55 tests covering all acceptance criteria.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>