Adds a new environment variable that lets users opt out of the
frecency-weighted ordering in favour of plain "most recently used"
ordering, addressing #1231.
- frecency (default) keeps the existing rank-times-recency-bucket score
- recency uses last_accessed directly, so popularity from months ago
never beats a directory you just visited
The displayed `--score` value stays the frecency value in both modes so
existing tooling around `zoxide query --score` is unaffected, and the
on-disk format is unchanged.
Signed-off-by: ChrisJr404 <chris@hacknow.com>