The httpx library renamed 'proxies' to 'proxy' in version 0.28.0.
This updates the fetch server to use the new parameter name and
removes the version cap on httpx.
Fixes#3287
Add comprehensive test coverage for the fetch server:
- TestGetRobotsTxtUrl: 6 tests for URL parsing
- TestExtractContentFromHtml: 3 tests for HTML-to-markdown conversion
- TestCheckMayAutonomouslyFetchUrl: 5 tests for robots.txt handling
- TestFetchUrl: 6 tests for URL fetching with various scenarios
Total: 20 tests covering:
- URL parsing and robots.txt URL generation
- HTML content extraction and markdown conversion
- robots.txt permission checking (401, 403, 404, allow/disallow)
- HTTP response handling (success, errors, raw mode)
- Proxy support
Also adds pytest and pytest-asyncio as dev dependencies.
