Fix WebSocket proxy implementation issues

[Copilot]

Addresses code review feedback on #32. The original implementation had critical bugs preventing WebSocket upgrades and lacked TLS support for wss:// connections.

Critical Fixes

HTTP version formatting - Request line was malformed using Debug format:

// Before: outputs "GET / Http11\r\n" (invalid)
format!("{} {} {:?}\r\n", req.method(), path, req.version())

// After: outputs "GET / HTTP/1.1\r\n" (valid)
format!("{} {} {}\r\n", req.method(), path, version_str)

TLS/WSS support - Added secure WebSocket handling:

• Detect wss:// scheme via is_schema_secure()
• Establish TLS handshake before WebSocket upgrade
• Updated tunnel_websocket_forward to accept EitherTlsStream

Header parsing - Fixed response header parsing to handle colons in values using find(':') instead of split_once(':')

Code Quality

• Extracted is_websocket_upgrade() helper to eliminate duplication
• Removed unused send_request_no_cache function
• Improved error handling with explicit validation instead of unwrap_or("")
• Corrected HTTP/2 and HTTP/3 version strings per RFC specs

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