Remove `components` and `ancestry`, and make `prune_dirs` Path-only

Part of: #1409

Depends on: #6809.

## Problem

`beets.util.components`, `beets.util.ancestry`, and the byte-compatible `prune_dirs` implementation duplicate behavior that `Path` already provides. Keeping these helpers after runtime paths are Path-native makes utility code harder to reason about and leaves another place where bytes can enter filesystem logic.

## Expected behavior

- Replace `components` callers with `Path.parts` or equivalent local `Path` operations.
- Replace `ancestry` callers with `Path.parents` or equivalent local `Path` operations.
- Make `prune_dirs` accept `Path` for both the target directory and optional root.
- Keep clutter matching behavior unchanged.
- Remove tests that only validate the deleted compatibility helpers, while preserving coverage for the behavior that still exists.

## Suggested fix

Remove the obsolete decomposition helpers first, then simplify `prune_dirs` around `Path.exists`, `Path.iterdir`, `Path.parents`, and `shutil.rmtree`.

## Acceptance criteria

- No production or test code imports `components` or `ancestry`.
- `prune_dirs` callers pass `Path`.
- Directory pruning behavior remains covered by tests.
- `poe test` and `poe lint` pass with coverage at or above 80%.

Search production and test code for beets.util.components, beets.util.ancestry, and prune_dirs, then trace the existing directory-pruning tests and callers. Replace the helper usage with Path operations, keep clutter matching and pruning behavior covered, and run poe test and poe lint with at least 80% coverage.

Written by the indexing model from the issue text.