rtla: Report missed event count

Print how many events were missed by trace buffer overflow in the main
instance at the end of the run (for hist) or during the run (for top).

Cc: John Kacur <jkacur@redhat.com>
Cc: Luis Goncalves <lgoncalv@redhat.com>
Link: https://lore.kernel.org/20250123142339.990300-5-tglozar@redhat.com


Signed-off-by: Tomas Glozar <tglozar@redhat.com>
Tested-by: Gabriele Monaco <gmonaco@redhat.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>