net/disk_cache/sql: Support entry creation on write in PersistentStore

This CL updates SqlPersistentStore and its internal backend classes to
support creating a new entry in the database during write operations.

Previously, `WriteEntryData` and `WriteEntryDataAndMetadata` required
an existing `ResId`. Now:
- `WriteEntryData` accepts a `ResIdOrTime` variant. If a `base::Time`
  is provided, it creates a new entry with that creation time.
- `WriteEntryDataAndMetadata` accepts an `std::optional<ResId>`. If
  `std::nullopt` is passed, it creates a new entry.

This is a foundational step for implementing lazy entry creation in the
SQL backend, allowing the actual database insertion to be deferred
until data is written or the entry is closed. Lazy entry creation will
be implemented in https://crrev.com/c/7532735.

Bug: 479348720
Change-Id: I01ce2c6712f629ec0471f4c25faa8b95b4f9e860
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7544748
Reviewed-by: Nidhi Jaju <nidhijaju@chromium.org>
Reviewed-by: Maks Orlovich <morlovich@chromium.org>
Commit-Queue: Tsuyoshi Horo <horo@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1581251}
NOKEYCHECK=True
GitOrigin-RevId: 2288d17407947287ffa4ebc9ca067296004b439d