* fix: add reqwest dependency to transport-streamable-http-client feature
- Fix compilation error when using transport-streamable-http-client feature due to missing dependency
- Move From<reqwest::Error> implementation to reqwest module
* feat(rmcp): enhance transport features by decoupling reqwest
- Added reqwest features for reqwest-based implementations.
- Updated documentation
- Modified error handling in SSE transport to use `String` for content type.
- Updated examples to include new features
* feat(rmcp): enhance transport features by decoupling reqwest
- Added reqwest features for reqwest-based implementations
- Updated documentation
- Modified error handling in SSE transport to use `String`
- Updated examples to include new features
