fix: used to sometimes report incorrect raft term immediately after restarting
fix: use picodata's system connection pool for CAS requests
fix: unify which term is used for cas predicates
CAS predicates should always contain the current raft term, because this is what's explicitly checked in proc_cas.
Note that this will sometimes result in a EntryTermMismatch error because the latest applied entry may have a different term in case the election has started but not finished yet.
We could add this check to all the client cas precondition checks, but it's not a big deal, because we handle the situation correctly anyways.
refactor: move wait_index into compare_and_swap
refactor: compare_and_swap now accepts a deadline instead of a timeout
refactor: massage compare_and_swap a bit
fix: unify all places where we call compare_and_swap and wait for the result
fix: check if DdlPrepare was rolled back before waiting for DdlCommit
Rolled back as in raft log roll back, which can happen when a leader changes to one who doesn't have the entry we persisted. Not to be confused with DdlAbort.
fix: cas requests are always reconstructed before retrying
fix: TermMismatch was always retriable, when did it stop?
doc: add comments to retriable error codes explaing why they are retriable