Python: improve agent samples and chat history handling

[eavanvalkenburg]

Motivation and Context

When passing the same object to agent.reduce_history as is present in the history_reducer attribute of the agent that the function doesn't accurately behave. This fixes that.

Also updates the sample to be a bit more concise.

Also fixes the way the single_dispatch is setup in ChatHistory.

Also ensures system/developer messages are not reduced away as that might impact performance.

The reduce_history method was removed from the agent base class, in favor of having the caller manage the change history and reduction as needed. The reduce_history was added to the agent group chat, as the chat history is managed internally as agents are invoked.

Description

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

[markwallace-microsoft]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
semantic_kernel/agents
agent.py	57	1	98%	82
semantic_kernel/agents/chat_completion
chat_completion_agent.py	102	7	93%	82, 85, 94–99, 124, 188
semantic_kernel/agents/group_chat
agent_chat.py	124	2	98%	78, 171
agent_group_chat.py	114	12	89%	70, 160, 210, 214–224
semantic_kernel/contents
chat_history.py	174	6	97%	103, 108, 263, 272, 283–284
semantic_kernel/contents/history_reducer
chat_history_reducer.py	29	9	69%	55–63
chat_history_reducer_utils.py	98	12	88%	103–105, 165–166, 181–186, 199, 204–205
chat_history_summarization_reducer.py	71	7	90%	96–97, 122–123, 130, 138, 171
chat_history_truncation_reducer.py	30	3	90%	50–53, 69
TOTAL	17074	1857	89%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
3039	4 💤	0 ❌	0 🔥	1m 30s ⏱️