test: add logger unit tests

[MD-Mushfiqur123]

Closes #400

Adds test_logger_globals.py with 21 tests covering:

• Global get_logger/set_log_level/set_cp_client functions
• Level gating (heartbeat/track/fire suppressed by default, shown when enabled)
• Structured output through execution context
• Internal methods: _normalize_level, _now_iso, _merge_attributes, _build_execution_record
• warning alias
• set_level runtime

cd sdk/python && python3 -m pytest tests/test_logger_globals.py -v
21 passed

PR generated by AI agent.

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