This PR fixes the "intra-node tablet migration" issue from the [LWT over tablets spec](https://docs.google.com/document/d/1CPm0N9XFUcZ8zILpTkfP5O4EtlwGsXg_TU4-1m7dTuM/edit?tab=t.0#heading=h.uk3mizf7gvs1). We make `get_replica_lock` to acquire locks on both shards to avoid races. We also implement read_repair for paxos state -- if `load_paxos_state` returns different states on two shards, we 'repair' it by choosing the values with maximum timestamp and writing the 'repaired' state to both shards.
LWT for tablets is not enabled yet. It requires migrating paxos state to colocated tablets, which is blocked on [this PR](https://github.com/scylladb/scylladb/pull/22906).
Regarding testing:
* We could possibly arrange a test case for the locking commit through some error injection magic. We'll return to this when LWT for tablets is enabled.
* We can't think of a clear test case for the read_repair commit. Any suggestions are welcome (@gleb-cloudius).
Backport: no need, since it's a new feature.
Closesscylladb/scylladb#24478
* https://github.com/scylladb/scylladb:
paxos_state: read repair for intranode_migration
paxos_state: fix get_replica_lock for intranode_migration
cc8c618356