[YCQL] Check correctness of picking read time for non transactional operations before conflict resolution

[pkj415]

Jira Link: DB-8295

Description

As seen in #19407, read time should not be picked until conflict resolution is successful for the non-transactional
operation path. This is because ResolveOperationConflicts() doesn't check regular db for
conflicting data committed in regular db. If in future, we have to read data before conflict
resolution, we should check conflicts in regular db too.

Once #19407 is fixed, YSQL ensures that all single-shard operations avoid picking a read time in the query layer. YCQL still picks read times in the query layer for non-transatcional operations. We should check if similar correctness issues can occur in YCQL, and if so, avoid picking a read time on the YCQL query layer. Once this is done, enable the RSTATUS_DCHECK(!read_time_, IllegalState,, ....) in WriteQuery::DoExecute() that has been commented out with this gh issue number.

Issue Type

kind/bug

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