tests/perf_fast_forward: disable partition-level fast-forwarding if not needed
tests/perf_fast_forward: disable partition-level fast-forwarding if not needed

Several of the test cases in perf_fast_forward do not need
partition-level fast-forwarding. However, since the defaults are used to
construct most of the readers the fast-forwarding is enabled regardless.

This showed an apparent regression in the perf_fast_forward results
after adcb3ec20ccd3e8ecda7b9ddac81671e2eb47f3a ("row_cache: read is not
single-partition if inter-partition forwarding is enabled") which
disabled an optimisation that was invalid when partition-level
fast-forwarind was requested.

This patch ensures that all single-partition reads that do not need
partition-level fast-forwarding keep it disabled.

scylladb/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla