Python: Move to a thinner wrap for Bedrock Agent in Python

[TaoChenOSU]

Motivation and Context

Though the current Bedrock agent implementation uses a "thin wrap" approach, it still has some abstractions that we don't want to maintain. Just like what we have done for the other agents, we remove those abstractions.

Description

1. Update the Bedrock agent abstraction to be thinner.
2. Update samples and tests.

Note: The .Net implementation doesn't need to be updated as it was already using a thinner wrap.
Note: This breaks the current usage pattern for Bedrock agents in Python.

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/bedrock
bedrock_agent.py	202	34	83%	101, 210, 242, 261, 277–280, 286, 288, 291, 295, 327, 357–366, 377, 409, 426–427, 429–430, 472, 483–484, 496, 532–543, 554, 571–584
bedrock_agent_base.py	141	41	71%	101, 119–120, 145, 158–160, 187, 206–208, 213, 232–234, 239, 243–244, 264–266, 275, 294–298, 303, 322–326, 331, 343–345, 357–376
semantic_kernel/connectors/ai/bedrock/services
bedrock_chat_completion.py	136	14	90%	117, 139, 164, 168–171, 229, 247–266, 325
bedrock_text_completion.py	57	2	96%	95, 118
bedrock_text_embedding.py	45	1	98%	94
semantic_kernel/connectors/ai/bedrock/services/model_provider
utils.py	74	20	73%	63, 66, 97, 101–112, 129–147, 168–171
TOTAL	18981	2406	87%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
3172	5 💤	0 ❌	0 🔥	1m 44s ⏱️