Optimize utils.py for Better Performance

[putbullet]

Updated utils.py to make CSV-to-SQLite conversion faster and cleaner, keeping it compatible with cli.py and existing tests. No overlap with open PRs (#85, #71, #49, #45).

Changes:

Added chardet to detect CSV encoding in load_csv, cutting down file reads.
Switched to pathlib.Path.rglob in csvs_from_paths for quicker directory scanning.
Used INSERT OR IGNORE in LookupTable.id_for_value to speed up SQL operations.
Generated CREATE TABLE SQL directly in get_create_table_sql, skipping in-memory DB.
Dropped six for Python 3 string handling.
Added context managers for SQLite connections to avoid leaks.

Added chardet to requirements.txt. No changes to cli.py. Should pass existing tests, but I can add new ones if needed. Let me know what you think!