Fix parent ignore matching for multiple explicit roots

[markusylisiurunen]

Fixes #3320.

This fixes an order-dependent bug in parent ignore matching when ripgrep is given multiple explicit search roots.

The root cause was in Ignore::add_parents. Absolute-parent matchers were cached only by ancestor directory path, but they also carried root-specific state in absolute_base. When a later explicit root reused a cached matcher built for an earlier root, parent ignore rules could be evaluated relative to the wrong root, which made .rgignore / parent ignore behavior depend on the order of the explicit roots.

The fix keeps the existing per-directory cache, but stops reusing the cached matcher node directly across roots. Instead, on a cache hit, it rebinds the current parent chain and absolute_base while reusing the compiled matcher data. The cache entry is then refreshed to keep reuse working across successive roots.

Tests added:

• a low-level regression in crates/ignore/src/dir.rs covering reuse across multiple explicit roots
• a traversal regression in crates/ignore/src/walk.rs covering both root orders

Validation:

• cargo test -p ignore
• repro from Order-dependent .rgignore bug with multiple explicit search roots #3320 now behaves correctly in both single-threaded and parallel runs