when using clone with --follow and --filter

Postgres 17.6 added \restrict and \unrestrict metacommands to pg_dump to
mitigate a security issue. This code skips these lines when restoring
roles.

17.6 release: https://www.postgresql.org/docs/17/release-17-6.html#RELEASE-17-6-CHANGES
CVE: https://www.postgresql.org/support/security/CVE-2025-8714/

Caused by using commands that support filter after ones that don't, or vice versa. For example, snapshot then clone --filter or clone --filter then stream sentinel. Try to deduce which filters should be used or give an error when that isn't straightforward.

When calling snapshot then using the snapshot id with `clone --follow
--snapshot` the code fails with "BUG: call to pgsql_commit() without holding an open multi statement connection"

`clone_and_follow` calls `copydb_fetch_schema_and_prepare_specs` which calls
`copydb_prepare_snapshot` since `specs->sourceSnapshot.state` is initially `SNAPSHOT_STATE_UNKNOWN`. `copydb_fetch_schema_and_prepare_specs` later calls `copydb_close_snapshot` which commits the transaction and sets the snapshot state to `SNAPSHOT_STATE_CLOSED`

`clone_and_follow` later calls `start_clone_process` which calls `cloneDB` which calls `copydb_fetch_schema_and_prepare_specs` again. This time `specs->sourceSnapshot.state` is `SNAPSHOT_STATE_CLOSED` so `copydb_prepare_snapshot` is not called. The code later tries to set the search path, which fails with a warning, then tries to commit the transaction, which fails with this error since no transaction was opened.

`copydb_prepare_snapshot` checks if the source snapshot state is `SNAPSHOT_STATE_UNKNOWN` or `SNAPSHOT_STATE_CLOSED` in order to prepare the snapshshot and open a transaction.
`copydb_fetch_schema_and_prepare_specs` on the other hand, only calls `copydb_prepare_snapshot` if the snapshot state is `SNAPSHOT_STATE_UNKNOWN`.
This code changes `copydb_fetch_schema_and_prepare_specs` to match `copydb_prepare_snapshot` and call it in either state.