Initial MPPT testbench: unified CLI for IT6500D + Prodigit 3366G + HIOKI 3193-10

Combines three instrument drivers (as git submodules) into a single
testbench for MPPT tracker efficiency testing. Features:
- Voltage sweep and load current sweep with CSV export
- Auto-range aware meter polling (waits for HIOKI to settle)
- Supply keepalive during long meter waits to prevent USB-TMC timeouts
- Live monitoring with real-time 4-panel matplotlib graphs
- Safe shutdown (load first, then supply)
- Post-sweep returns to 75V idle with supply ON

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitignore

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+__pycache__/
+*.pyc
+*.egg-info/
+dist/
+build/
+.venv/
+*.csv