rtla: Introduce common_threshold_handler() helper

rtla: Introduce common_threshold_handler() helper

Several functions duplicate the logic for handling threshold actions.
When a threshold is reached, these functions stop the trace, perform
configured actions, and restart the trace if --on-threshold continue
is set.

Create common_threshold_handler() to centralize this shared logic and
avoid code duplication. The function executes the configured threshold
actions and restarts the necessary trace instances when appropriate.

Also add should_continue_tracing() helper to encapsulate the check
for whether tracing should continue after a threshold event, improving
code readability at call sites.

In timerlat_top_bpf_main_loop(), use common_params directly instead
of casting through timerlat_params when only common fields are needed.

Signed-off-by: Wander Lairson Costa <wander@redhat.com>
Link: https://lore.kernel.org/r/20260309195040.1019085-5-wander@redhat.com
Signed-off-by: Tomas Glozar <tglozar@redhat.com>