probe plotting feature request

Two small plotting additions would close a usability gap we keep hitting when people cross-check our figures against Cambridge NeuroTech's hard-copy datasheets:

1. Shank-ID labels.
   When a probe has multiple shanks, it would help to optionally annotate each shank with its shank ID (e.g. "A", "B" / 0, 1, ...) on the plot_probe / plot_probegroup output. Today the shanks are drawn but unlabelled, so a reader has to infer which shank is which - and people's assumptions about where "Shank A" sits differ, which causes real confusion.

2. Front/back orientation label for dual-sided probes.
   both faces are rendered from a front-facing viewpoint (the back face mirrored into the front view). But it is not explicit.
   A short built-in label / title addition such as "back - viewed from front" on the back sides's panel would make the orientation unambiguous against Cambridge's printed documentation, where the back is sometimes drawn viewed from the back.

A simple optional kwarg on plot_probe for each (e.g. with_shank_ids=True and an orientation caption for side="back") would be enough - no change to default behaviour.

Start at the plot_probe and plot_probegroup entry points and inspect how shanks and dual-sided probe faces are rendered. Add optional shank-ID annotations and a back-face orientation caption without changing default behavior, then verify plots for multi-shank and dual-sided probes.