fix: Generate deterministic equipment IDs to prevent 404 errors on reconnection

[X9X0]

Problem

Equipment IDs were being generated using random UUIDs (uuid.uuid4()), causing them to change every time a device reconnected or the server restarted. This resulted in 404 errors when clients tried to access equipment endpoints (like /api/equipment/{equipment_id}/readings) using stale IDs from before the reconnection.

Example scenario:

1. Device connects → assigned ID ps_61ee82b9
2. Client stores this ID and makes requests
3. Device disconnects/reconnects → assigned NEW ID ps_a1b2c3d4
4. Client requests to /api/equipment/ps_61ee82b9/readings → 404 Not Found

Solution

Implemented deterministic equipment ID generation using SHA256 hashing of the VISA resource string:

• Added generate_equipment_id() helper function in server/equipment/base.py
• Uses SHA256 hash of resource string to create stable, deterministic IDs
• Updated all equipment classes to use the new helper:
  • BK Precision power supplies
  • Rigol oscilloscopes (MSO2072A, DS1104, DS1102D)
  • Rigol electronic loads (DL3021A)
  • All mock equipment classes

Result: Equipment with resource string ASRL/dev/ttyUSB0::INSTR will always get ID ps_56fdd3df, regardless of reconnections or server restarts.

Changes

• server/equipment/base.py: Added generate_equipment_id() function
• server/equipment/bk_power_supply.py: Use deterministic IDs
• server/equipment/rigol_scope.py: Use deterministic IDs (all 3 scope classes)
• server/equipment/rigol_electronic_load.py: Use deterministic IDs
• server/equipment/mock/*.py: Use deterministic IDs for all mock equipment

Testing

Verified that equipment IDs remain stable:

# Connect device
→ {"equipment_id":"ps_56fdd3df","status":"connected"}

# Disconnect and reconnect
→ {"equipment_id":"ps_56fdd3df","status":"connected"}  # SAME ID ✓