CASSGO-22 Dont mutate Query/Batch

Currently queries are mutated while being executed, the query metrics and the consistency are both changed. Instead move query metrics to the Iter and remove the need to change the queries consistency for speculation.

The issue names Query, Batch, Iter, query metrics, consistency, and speculation but no files or tests. Trace where Query and Batch execution mutates metrics or consistency, then identify the Iter path and define completion as execution no longer mutating queries while metrics remain available and speculation still works.

Written by the indexing model from the issue text.