perf test: Add sched latency and script shell tests

Add shell tests covering the `perf sched latency` and `perf sched
script` commands. The test creates 2 noploop processes on the same
forced CPU, it then checks that the process appears in the `perf
sched` output.

Reviewed-by: James Clark <james.clark@linaro.org>
Signed-off-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20250628012302.1242532-2-irogers@google.com


Signed-off-by: Namhyung Kim <namhyung@kernel.org>