Add info log for shm processing in `ldshm` CLI cmd

Log shm file name and detected period before null segment
processing to aid debugging.

(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code

piker/storage/cli.py

@@ -294,6 +294,11 @@ def ldshm(
                             f'Something is wrong with time period for {shm}:\n{times}'
                         )
                 period_s: float = float(max(d1, d2, med))
+                log.info(
+                    f'Processing shm buffer:\n'
+                    f'  file: {shmfile.name}\n'
+                    f'  period: {period_s}s\n'
+                )
 
                 null_segs: tuple = tsp.get_null_segs(
                     frame=shm.array,