test: add unit tests for BedrockClassifier

[hashwnath]

Addresses #448

Adds comprehensive unit tests for BedrockClassifier covering:

• Initialization: client injection, boto3 auto-creation, default/custom model ID, inference config defaults and overrides
• Tool schema structure: validates the analyzePrompt tool spec shape and required fields
• Classification flow: happy path agent selection, confidence conversion, toolChoice behavior for anthropic vs non-anthropic models, custom inference config propagation
• Error handling: no output, empty tool use, invalid tool input, BotoCoreError, ClientError
• Callbacks: verifies on_classifier_start and on_classifier_stop are invoked with correct arguments

Follows existing test patterns from test_anthropic_classifier.py (pytest, MockAgent, @patch, @pytest.mark.asyncio).

All 22 tests pass.