refactor(security): move all database access into pkg/security/lookup

pkg/security no longer contains SQL. Every provider calls a store interface
from lookup, implemented by a procedure backend (Postgres stored procedures,
the default there) and a direct backend (dialect-driven SQL for postgres,
sqlite, mysql and mssql with configurable table and column names).

- add sectypes, lookup, lookup/{dialect,procedure,direct,backends,ddl,conformance}
- split totp and providers sub packages out of the core package
- replace SQLNames/TableNames/QueryMode with lookup.Config (see breaking_changes.md)
- direct backend now covers column/row security and API-key login
- move txsettings SQL to lookup.ApplyTxSettings; remove password.go
- move schema scripts under lookup/, add reference DDL per dialect
- add a shared conformance suite; run it on sqlite, and on Postgres in a
  podman/docker container (RESOLVESPEC_TEST_CONTAINERS=1)
- fix procedure schema bugs found on real Postgres: duplicate p_data
  parameter, JSON null arrays, expires_at timezone casts, passkey list
  GROUP BY, missing resolvespec_passkey_login; accept zone-less timestamps

pkg/common/adapters/database/pgsql.go

@@ -223,6 +223,11 @@ func (p *PgSQLAdapter) GetUnderlyingDB() interface{} {
 	return p.db
 }
 
+// SQLDB implements common.SQLDBProvider.
+func (p *PgSQLAdapter) SQLDB() *sql.DB {
+	return p.db
+}
+
 func (p *PgSQLAdapter) DriverName() string {
 	return p.driverName
 }