⚡ Optimize folder lookups with in-memory caching

[yj9404]

This PR implements in-memory caching for folder lookups in create_worklog.py to reduce redundant API calls to Confluence.

💡 What:

• Introduced a module-level _FOLDER_CACHE dictionary to store folder lists for each parent_id.
• Modified get_folder_id_by_name to prioritize cache lookups and populate the cache on the first fetch.
• Updated find_or_create_folder to append newly created folders to the cache, ensuring consistency without additional API calls.

🎯 Why:

The script frequently checks for the existence of folders (Year, Month) that it might have already looked up or created earlier in the same execution. Caching these results eliminates unnecessary GET requests and potentially redundant POST attempts if the lookup failed but a previous create succeeded.

📊 Measured Improvement:

Using a benchmark script that simulates a run for December 30, 2025 (which involves checking current year/month, next year/month, and Thursday's year/month folders), the following improvements were observed:

• GET calls: Reduced from 7 to 2 (71.4% improvement).
• POST calls: Reduced from 8 to 5 (37.5% improvement).
• Execution Time: Slightly reduced due to fewer network simulations (0.0085s to 0.0055s in a mock environment).

All existing tests in test_create_worklog.py have been updated to account for the caching behavior and pass successfully.

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PR created automatically by Jules for task 11118709063343959285 started by @yj9404

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