Add a BAMBUDDY_VP_DUMP_WIRE=1 escape hatch that writes the bridge's
cached push_status (in) and the 1Hz slicer-facing copy (out) to
<log_dir>/vp_wire/<vp_name>_<direction>.json, overwritten each tick.
#1622's symptom — empty filament dropdown in slicer's AMS slot details
for P1S/A1 but not H2D in non-proxy VP modes — needs visibility into
the actual wire bytes flowing through the bridge to bisect between
"cache is missing fields" and "_send_status_report strips them on copy."
The existing logs prove the bridge is bound and pushing at 1Hz, but
not what's in the payload.
Off by default, single env flag, single file per VP per direction
(bounded disk footprint), failures swallowed at debug so a broken
dump can never break the 1Hz loop. 21 tests pin the helper contract:
disabled-by-default, atomic writes, sanitized vp_name (no path
escape), per-call env check so toggling without restart works.
