Addresses review: agents that leave streaming unset (None) should get the
default StreamingHandler, not polling. Only agents that explicitly set
streaming=False trigger the polling fallback.
When the remote agent advertises streaming=False in its capabilities,
the client now falls back to PollingHandler instead of always using
StreamingHandler. This fixes connection failures when delegating to
non-streaming A2A servers.
* feat: add server-side auth schemes and protocol extensions
- add server auth scheme base class and implementations (api key, bearer token, basic/digest auth, mtls)
- add server-side extension system for a2a protocol extensions
- add extensions middleware for x-a2a-extensions header management
- add extension validation and registry utilities
- enhance auth utilities with server-side support
- add async intercept method to match client call interceptor protocol
- fix type_checking import to resolve mypy errors with a2aconfig
* feat: add transport negotiation and content type handling
- add transport negotiation logic with fallback support
- add content type parser and encoder utilities
- add transport configuration models (client and server)
- add transport types and enums
- enhance config with transport settings
- add negotiation events for transport and content type
* feat: add a2a delegation support to LiteAgent
* feat: add file input support to a2a delegation and tasks
Introduces handling of file inputs in A2A delegation flows by converting file dictionaries to protocol-compatible parts and propagating them through delegation and task execution functions. Updates include utility functions for file conversion, changes to message construction, and passing input_files through relevant APIs.
* feat: liteagent a2a delegation support to kickoff methods
