Users/axsuarez/serialization fix

[axelsrz]

This pull request includes multiple changes to the Botbuilder and Core libraries, as well as a test sample. The changes focus on improving type hints, imports, and method calls, as well as adding new configurations and optional fields.

Improvements to type hints and imports:

• libraries/Botbuilder/microsoft-agents-botbuilder/microsoft/agents/botbuilder/channel_service_adapter.py: Removed the unused Protocol import and updated the ConnectorClientBase and UserTokenClientBase imports to include ConnectorClient and UserTokenClient. [1] [2]
• libraries/Core/microsoft-agents-core/microsoft/agents/core/models/conversation_reference.py: Added Optional import from typing to handle optional fields.

Method call improvements:

• libraries/Botbuilder/microsoft-agents-botbuilder/microsoft/agents/botbuilder/channel_service_adapter.py: Updated send_to_conversation method call to use activity.model_dump(by_alias=True, exclude_unset=True) to ensure only set fields are included.
• libraries/Botbuilder/microsoft-agents-botbuilder/microsoft/agents/botbuilder/channel_service_adapter.py: Added type hints for connector_client and user_token_client and ensured they are properly closed after use. [1] [2] [3]

Configuration and optional fields:

• libraries/Core/microsoft-agents-core/microsoft/agents/core/models/_agents_model.py: Added populate_by_name = True to the Config class to enable population of fields by their name.
• libraries/Core/microsoft-agents-core/microsoft/agents/core/models/conversation_reference.py: Updated activity_id and locale fields to be optional.

Test sample updates:

• test_samples/echo_bot/app.py: Replaced web.Application and web.run_app with Application and run_app from aiohttp.web for consistency and clarity. [1] [2]