kvserver: use termCache for term lookup after raftLog compaction

After implementing "`termCache`" , #136296
we can also make [this term lookup](https://github.com/cockroachdb/cockroach/blob/e87c8bdbce0486f00c3adcdffc850ea2becfd0dc/pkg/kv/kvserver/batcheval/cmd_truncate_log.go#L80) go through the term cache first.

Currently LogSnapshot() operates when both `Replica.mu` and `Replica.raftMu `are held. While GetTerm only holds `Replica.mu`.
Something to consider when implementing. May not be doable, needs investigation.

Start in pkg/kv/kvserver/batcheval/cmd_truncate_log.go at the linked term lookup, then read the termCache implementation from issue #136296 and inspect GetTerm and LogSnapshot lock requirements. Determine whether the lookup can safely consult termCache after raft log compaction; done means the safe cache-first path is implemented, or the investigation establishes why it cannot be used.

Written by the indexing model from the issue text.