rtla: Count all processed events

rtla: Count all processed events

Add a field processed_events to struct trace_instance and increment it
in collect_registered_events, regardless of whether a handler is
registered for the event.

The purpose is to calculate the percentage of events that were missed
due to tracefs buffer overflow.

Cc: John Kacur <jkacur@redhat.com>
Cc: Luis Goncalves <lgoncalv@redhat.com>
Cc: Gabriele Monaco <gmonaco@redhat.com>
Link: https://lore.kernel.org/20250123142339.990300-3-tglozar@redhat.com
Signed-off-by: Tomas Glozar <tglozar@redhat.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>