chore: remove dead *ActivityInput classes for inbound-only types

[rajan-chari]

Summary

Follow-up to #340. Deletes 7 *ActivityInput classes that were removed from the ActivityParams union and have zero references anywhere in the codebase.

Deleted classes:

• MessageDeleteActivityInput
• MessageUpdateActivityInput
• ConversationUpdateActivityInput
• HandoffActivityInput
• TraceActivityInput
• CommandSendActivityInput
• CommandResultActivityInput

The corresponding *Activity classes (used as handler type hints for incoming events) are preserved.

Why

These classes existed for model symmetry (every Activity type had an Input counterpart) but represented inbound-only event types. They had no valid outbound send path and no references outside their own definitions and __init__.py exports. Removing them eliminates the suggestion that these types are constructible for any purpose.

Test plan

Automated

• CI passes: build, lint (ruff + pyright), and unit tests on Python 3.12/3.13/3.14
• Local: 552 tests pass on Python 3.13

Verification

• from microsoft_teams.api.activities import MessageDeleteActivityInput raises ImportError
• from microsoft_teams.api.activities import MessageDeleteActivity still works
• All handler decorators (@app.on_message_delete, @app.on_message_update, etc.) still work with incoming Activity types

🤖 Generated with Claude Code

[rajan-chari]

Manual Test Results — Echo Bot (Python)

Tested on branch fix/338-rename-activity-params (PR #342, which stacks on this PR), commit bf62a5c. Python echo bot deployed to BAMI1 tenant via DevTunnel.

#	Test	Result	Details
1	Send a message → bot replies	PASS	MessageActivityInput via ctx.send(str) works after dead class removal
2	Bot shows typing indicator before reply	PASS	TypingActivityInput still works
3	Edit a sent message → @app.on_message_update fires	PASS	Incoming MessageUpdateActivity handler unaffected by removed *ActivityInput classes
4	Delete a message → @app.on_message_delete fires	PASS	Incoming MessageDeleteActivity handler unaffected by removed *ActivityInput classes
5	No regression in send/typing	PASS	Removed input classes were inbound-only — no impact on send path

All 5 test steps passed. Removing the dead *ActivityInput classes for inbound-only types causes no regressions.

[lilyydu]

added comment here #340 (comment)

[lilyydu]

closing to handle all changes in #340