net/disk_cache/sql: Implement entry dooming and deletion

This change implements the fundamental operations for dooming and
deleting cache entries in `SqlPersistentStore`, the storage layer for
the new SQL-based disk cache backend.

The following methods have been added:
- DoomEntry: Marks an entry for deletion by setting a `doomed` flag in
  the database. This logically removes the entry from the cache's size
  and entry count totals but leaves the data on disk until
  `DeleteDoomedEntry` is called.
- DeleteDoomedEntry: Physically removes a previously doomed entry from
  the `resources` table. This action does not alter the cache's size
  metadata, as that was adjusted during the dooming process.
- DeleteLiveEntry: Immediately and physically deletes an live
  (non-doomed) entry. This operation updates the cache size and entry
  count metadata accordingly.

All database modifications are performed within transactions to ensure
atomicity.

Bug: 422065015
Change-Id: Id9e059ba377ddab4a674472f3c0472b9adecf1b3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6647370
Reviewed-by: Maks Orlovich <morlovich@chromium.org>
Reviewed-by: Nidhi Jaju <nidhijaju@chromium.org>
Reviewed-by: Mingyu Lei <leimy@chromium.org>
Commit-Queue: Tsuyoshi Horo <horo@chromium.org>
Reviewed-by: Olivier Li <olivierli@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1477066}