Add relay indexing for existing notes
This patch introduces a relay index for new notes and notes that have
already been stored, allowing the database to track additional relay
sources for a given note.
Changes:
- Added `NDB_WRITER_NOTE_RELAY` to handle relay indexing separately from
new note ingestion.
- Implemented `ndb_write_note_relay()` and
`ndb_write_note_relay_kind_index()` to store relay URLs.
- Modified `ndb_ingester_process_event()` to check for existing notes
and append relay info if necessary.
- Introduced `ndb_note_has_relay()` to prevent duplicate relay entries.
- Updated LMDB schema with `NDB_DB_NOTE_RELAYS` (note_id -> relay) and
`NDB_DB_NOTE_RELAY_KIND` (relay + kind + created_at -> note).
- Refactored `ndb_process_event()` to use `ndb_ingest_meta` for tracking
relay sources.
- Ensured proper memory management for relay strings in writer thread.
With this change, nostrdb can better track where notes are seen across
different relays, improving query capabilities for relay-based data
retrieval.
Signed-off-by: William Casarin <jb55@jb55.com>
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