hil: fail-closed lock, usbtest retry history, shared harness scripts from agentrc at a pin (#4245)

The HIL board lock failed open when its lock dir was unusable; it now refuses. hil_report keeps per-case usbtest
statuses, skipped cells and earlier attempts (closes #4226). The lock mechanics, RTT console and bounded USB
observation are loaded from lib/agentrc at the commit tools/get_deps.py pins (hathach/agentrc#117, #121) through
test/hil/helper/agentrc.py; tinyusb's own copies and the superseded rtt plan and spec are gone.

Hardware: ci.lan lpcxpresso55s69 cdc_msc OK, usbtest 30/30, board_test OK at 48d49ef22 (hil-1792299100). Tests:
test/hil 470, change-impact 293, .claude/test 289. CI red only from 33 HIL cells accepted as rig-side.