feat: Add --map-root argument to configure repository map root directory

[coredevorg]

The patch makes the root directory for .aider.tags.cache.v3 configurable through an additional argument --map-root or AIDER_MAP_ROOTenvironment variable.

This becomes important if your project lives on a CIFS mount and you encounter:

Tags cache error: database is locked
Unable to use tags cache at /mnt/.../.aider.tags.cache.v3, falling back to memory cache
Cache recreation error: [Errno 11] Resource temporarily unavailable: 'cache.db'

With the --map-root parameter, the cache directory can be moved to local device to avoid the problem.