Support for httpx instrumentation

[virtualzx-nad]

Original issue: traceloop#2283

Problem:
Add instrumentation support for the httpx library to enable tracing of HTTP requests made through httpx.

Requirements:

1. Implement httpx instrumentation
2. Track request/response details
3. Capture timing information
4. Handle async operations correctly
5. Add appropriate error handling
6. Include tests and documentation

Difficulty: Beginner-friendly
Type: Feature