Add ExperimentalWarning class and indicate reactions and targeted messages as preview

[corinagum]

• ExperimentWarning is a subclass to FutureWarning so users supress preview API warnings if desired.
• @experimental("TEAMS0001") decorator - emits warnings when applied to a class or function
• Mark reactions and targeted messages as preview

Note that suppression is not granular - while C# differentiates between different diagnostics, the ignore below will suppres all preview warnings.

To suppress the warnings:

import warnings
from microsoft_teams.common.experimental import ExperimentalWarning

warnings.filterwarnings("ignore", category=ExperimentalWarning)

[Copilot]

Pull request overview

This PR introduces an ExperimentalWarning class and @experimental decorator to the microsoft_teams.common package, providing a mechanism to mark preview APIs with runtime warnings. It then applies these markers to two preview features: reaction support (ReactionClient) and targeted messages (create_targeted, update_targeted, delete_targeted, and with_recipient's is_targeted parameter).

Changes:

• New experimental.py module with ExperimentalWarning (subclass of FutureWarning) and the @experimental(diagnostic) decorator for both classes and async/sync functions.
• ReactionClient decorated with @experimental("TEAMS0001") and its docstring updated.
• ConversationActivityClient's three targeted methods decorated with @experimental("TEAMS0002"); ActivityInput.with_recipient and is_targeted field updated to emit the same warning.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
packages/common/src/microsoft_teams/common/experimental.py	New file: defines ExperimentalWarning and @experimental decorator
packages/common/src/microsoft_teams/common/__init__.py	Exports ExperimentalWarning and experimental from the package
packages/api/src/microsoft_teams/api/clients/reaction/client.py	Applies @experimental("TEAMS0001") to ReactionClient
packages/api/src/microsoft_teams/api/clients/conversation/activity.py	Applies @experimental("TEAMS0002") to targeted activity methods
packages/api/src/microsoft_teams/api/models/activity.py	Adds ExperimentalWarning emission to with_recipient when is_targeted is set; updates docstrings