feat: Add filters on the realtime subscriptions

[ivasilov]

Summary

• Adds Realtime postgres_changes filters derived from each active query's WHERE clause, so a subscribed table only receives rows relevant to the queries currently observing it (falling back to an unfiltered/catch-all subscription when a query's conditions can't be expressed as Realtime filters).
• Supports eq, neq, gt/gte/lt/lte (and their negations), in/not in, isNull/not isNull, and ANDed composite conditions, with PostgREST-safe value serialization (quoting, escaping) shared between the Realtime filter builder and the query builder.
• Fixes a race between the initial PostgREST fetch and Realtime events: INSERT/UPDATE now upsert into the collection instead of throwing when a row arrives out of the expected order.
• Adds an unfiltered UPDATE listener (so a row already in the collection keeps receiving updates after it stops matching a filter) and an unfiltered DELETE listener (Realtime only sends filtered deletes for tables with replica identity full).
• Channel subscriptions are now rotated/namespaced by topic instead of a fixed per-table name, and swapped in only after the replacement channel finishes subscribing, so no change is missed during a filter-set change.

Test plan

• pnpm test — 169 tests pass
• pnpm build — builds cleanly