0.12.0-rc.1

PostgreSQL 17/18/19(beta1) EXPLAIN compatibility + HypoPG fix.

- fix(pgexplain): support PG18 fractional Actual Rows (uint64->float64) and
  signed Query Identifier (int64) — explain was fully broken on PG18.
- feat(pgexplain): render PG18 fields (Disabled, Index Searches, WAL Buffers
  Full, Storage); broader node-type coverage; fix ModifyTable rendering.
- fix(hypo): query hypopg() directly instead of hypopg_list_indexes() (became a
  view in HypoPG 1.2.0; was failing with SQLSTATE 42883).
- ci: PG13-19beta1 EXPLAIN matrix + HypoPG integration test.