Remove unnecessary tuple; prepare for "iterator" verbiage

Remove unnecessary tuple; prepare for "iterator" verbiage

Remove a tuple surrounding a generator expression that
is immediately iterated in any case.   Additionally
note that the bulk methods can likely accept non-list
objects such as arbitrary iterables, however without test
coverage this is not yet guaranteed; use the term "sequence"
for now.

Also added a warmup to a cache key profiling test to get
consistent results.

Fixes: #5163
Change-Id: If838fe214da574763115855c1a65171533c96e64