Add PSR-18 HTTP Client, PSR-17 Factories, URI Implementation & Performance Optimizations

[yordadev]

Summary

Major feature release adding PSR-18 HTTP Client support, PSR-17 Factory implementations, full URI interface, and significant performance optimizations to the signalforge_http C extension.

New Features:

• PSR-18 compliant HTTP Client with libcurl backend
• HttpRequestPool for concurrent request execution with thread pool
• PSR-17 Factory implementations (RequestFactory, ResponseFactory, StreamFactory, UriFactory, etc.)
• Full PSR-7 UriInterface implementation with RFC 3986 compliance
• Connection sharing and keep-alive support
• Automatic retry with exponential backoff
• HTTP/2 and HTTP/3 support (when available)

Performance Optimizations:

• Header normalization caching for faster lookups
• getHeaders() array caching to avoid repeated rebuilds
• Interned strings for common header names (content-type, location)
• Increased stream buffer size (64KB → 256KB) for large payloads
• Optimized header lookup using simple lowercase conversion

Security Hardening:

• URI injection prevention (blocks CRLF, null bytes, control characters)
• Host header validation
• User info validation

Infrastructure:

• Fixed Dockerfile.valgrind to include --enable-signalforge-http-client
• Added examples/basic.php demonstrating all extension features
• Extended test suite from ~97 to 206 tests