Python: fix(bedrock): map guardrail_intervened and model_context_window_exceeded stop reasons (#14631)

### Motivation and Context

The Bedrock Converse API can end a turn with `guardrail_intervened` (a
configured guardrail blocked the output) or
`model_context_window_exceeded` (the model hit its context window).
`finish_reason_from_bedrock_to_semantic_kernel` only knew five of the
stop reasons, so for these two the message came back with
`finish_reason=None`, indistinguishable from an unrecognised value.

### Description

- `guardrail_intervened` maps to `FinishReason.CONTENT_FILTER`, same as
`content_filtered`.
- `model_context_window_exceeded` maps to `FinishReason.LENGTH`, same as
`max_tokens`.
- Unit tests for both mappings; they fail on `main` (the function
returns `None`) and pass with the change. The Bedrock unit test folder
passes.

### Contribution Checklist

- [x] The code builds clean without any errors or warnings
- [x] The PR follows the SK Contribution Guidelines
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

This change was made with Claude Code; the tests were run against `main`
and the branch.

Author: pcbeingused333

python/semantic_kernel/connectors/ai/bedrock/services/model_provider/utils.py

@@ -213,5 +213,7 @@ def finish_reason_from_bedrock_to_semantic_kernel(finish_reason: str) -> FinishR
         "end_turn": FinishReason.STOP,
         "max_tokens": FinishReason.LENGTH,
         "content_filtered": FinishReason.CONTENT_FILTER,
+        "guardrail_intervened": FinishReason.CONTENT_FILTER,
+        "model_context_window_exceeded": FinishReason.LENGTH,
         "tool_use": FinishReason.TOOL_CALLS,
     }.get(finish_reason)

python/tests/unit/connectors/ai/bedrock/services/test_bedrock_model_provider_utils.py

@@ -344,6 +344,18 @@ def test_finish_reason_from_bedrock_to_semantic_kernel_tool_use() -> None:
     assert reason == FinishReason.TOOL_CALLS
 
 
+def test_finish_reason_from_bedrock_to_semantic_kernel_guardrail_intervened() -> None:
+    """Test that 'guardrail_intervened' maps to FinishReason.CONTENT_FILTER"""
+    reason = finish_reason_from_bedrock_to_semantic_kernel("guardrail_intervened")
+    assert reason == FinishReason.CONTENT_FILTER
+
+
+def test_finish_reason_from_bedrock_to_semantic_kernel_context_window_exceeded() -> None:
+    """Test that 'model_context_window_exceeded' maps to FinishReason.LENGTH"""
+    reason = finish_reason_from_bedrock_to_semantic_kernel("model_context_window_exceeded")
+    assert reason == FinishReason.LENGTH
+
+
 def test_finish_reason_from_bedrock_to_semantic_kernel_unknown() -> None:
     """Test that unknown finish reason returns None"""
     reason = finish_reason_from_bedrock_to_semantic_kernel("something_unknown")