fix: Fix all failing test files with proper mocking and imports

- test_tiered_context.py: Fix aggregate imports to src.aggregate
- test_gemini_cli_adapter_parity.py: Fix subprocess.Popen mock path and JSON format
- test_gemini_cli_edge_cases.py: Fix mock path, JSON format, and adapter initialization
- test_gemini_cli_parity_regression.py: Fix mock path, reset global adapter
- test_token_usage.py: Fix SimpleNamespace mock structure for gemini response

project_history.toml

@@ -8,5 +8,5 @@ active = "main"
 
 [discussions.main]
 git_commit = ""
-last_updated = "2026-03-05T19:22:57"
+last_updated = "2026-03-05T20:14:45"
 history = []