Handle resuming tile cache downloads

[chrowe]

Summary

• detect existing tile caches and resume downloading only missing tiles instead of wiping the cache
• update tile processing notice handling and failure detection to work for both S3 and local cache paths
• add tests covering tile ID parsing and cache resumption

Testing

• pytest tests/test_tile_cache_resumption.py (fails: missing boto3 dependency in test environment; network access blocked when attempting to install)

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Codex Task

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Tile cache completeness check ignores S3 pagination

_has_incomplete_tile_cache determines whether to rebuild by listing existing tile files, but for S3 targets _list_existing_tile_filepaths delegates to _list_all_tiff_filepaths_in_s3_folder, which issues a single list_objects_v2 call (default 1,000 key limit). On caches with more than 1,000 tiles, completed_tile_ids will only include the first page of objects, so unretrieved_tiles stays non‑empty and the cache is always treated as incomplete even when fully populated, forcing unnecessary reprocessing for large cities.

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