Cardano Updates

The pool_relay encoder serialized the unsigned Word16 port as a signed
int2, so relay ports above 32767 wrapped to negative values
(port - 65536). The pool_relay.port SQL column is int4, so the wrapped
value was stored verbatim.

- Encode the port as int4 to match the column and preserve the full
  0-65535 range.
- Add migration-2-0049 to repair already-stored rows by adding 65536 to
  every negative port (no-op on a clean or freshly synced database).
- Add a cardano-db IO regression test that inserts a relay with port
  41950 and asserts it round-trips (fails with the old int2 encoder,
  reading back -23586).
- Give the chain-gen test relay a port > 32767 so the end-to-end pool
  path also exercises the full range.

The DB integration test suite now runs the groups concurrently:

 * Alonzo-era
 * Babbage-era
 * Conway-era
 * QSM (QuickCheck State Machine)

Concurrent tests cannot share a database, so each group has its own
copy. Grouping at the top level keeps the databases/threads manageable.

Also, add the required databases in the nix `preCheck` hook and GitHub
CI workflows.

Prerequisite for running tests concurrently.

All DB tests share the same database, so we can read the from the
`PGPASSFILE` environment variable. When we run them in parallel, this
won't be possible, since each running test will need its own database.

Instead, explicitly pass the `PGConfig` to all tests, which will allow
different database configs per test run.

The DB integration test suite now runs the groups concurrently:

 * Alonzo-era
 * Babbage-era
 * Conway-era
 * QSM (QuickCheck State Machine)

Concurrent tests cannot share a database, so each group has its own
copy. Grouping at the top level keeps the databases/threads manageable.

Also, add the required databases in the nix `preCheck` hook.

Previously, there were some tests that duplicated testLabels (copy/paste
errors). This is a prerequisite for running tests in parallel, as the
per-test state directory (`testfiles/temp/<testLabel>`) could have
collided.