Deduplicate and optimize the collection classes

[pfefferle]

Proposed changes:

Refactors includes/collection/ to remove duplication and cut complexity, keeping every public call site identical (composable traits via late static binding, static shape retained).

• Bug fix: Interactions::persist() attached an anonymous akismet_comment_nonce filter it never removed, leaking a closure per federated comment and forcing Akismet's nonce check to inactive for every later comment in the same request. Now a named method plus try/finally restores all four temporary filters on every path.
• Six new traits de-duplicate the copy-pasted patterns across the CPT-backed collections: recipient meta CRUD, paginated query() + get_by_authority(), object-title derivation, guid lookup, KSES-safe insert, and the batched purge loop.
• Followers::get_inboxes collapses a two-step query into a single JOIN (runs on every federation send).
• Remote_Actors actor serialization now suspends and restores only the mention/hashtag/link filters that were actually registered, at their original priority (fixes an unconditional re-add edge).
• Actors::get_id_by_resource replaces a sloppy scheme regex with wp_parse_url().
• Remote_Posts::get_by_remote_actor_id swaps deprecated meta_key/meta_value for a meta_query (drops two PHPCS suppressions).

Net roughly −435 lines across the collection classes, plus six small trait files. With_Guid_Lookup also drops a latent double-escape in Remote_Actors::get_by_uri (it ran esc_sql() inside prepare()), standardizing on the same esc_url_raw normalization used at write time.

Other information:

• Have you written new tests for your changes, if applicable?

New regression test asserts the comment filters/actions are fully restored after persist().

Testing instructions:

• Ensure the full PHP suite passes: npm run env-test (2760 tests green).
• Ensure PHP standards pass: composer lint (clean).
• Functional spot checks against trunk:
  • Receive a comment from the fediverse on a post, then submit a normal local comment, and confirm spam protection still applies to the local comment.
  • Follow and unfollow a remote actor; view followers and following lists with pagination.
  • Confirm inbox/outbox/remote-post cleanup (purge) still trims old items and preserves remote posts that have local comments.

Changelog entry

Changelog entry for the Akismet fix is included in the branch (.github/changelog/restore-akismet-nonce-after-federated-comment); the rest is internal refactor.