Add inventory tracking and restock maintenance for OT-2 color mixing

[Copilot]

Students were running experiments while paint colors (red/yellow) were out of stock. This adds MongoDB-based inventory tracking with evaporation compensation and Prefect maintenance flows for manual restocking.

Core System

• inventory_utils.py: MongoDB CRUD for R/Y/B stock levels with time-based evaporation (5 µL/hr default)
• restock_flow.py: Three Prefect flows - restock-maintenance, initialize-inventory, check-inventory-status
• device_with_inventory.py: New mix-color-with-inventory flow that validates stock before mixing and subtracts after

Integration

• Pre-mixing validation raises ValueError if insufficient stock (threshold + required volume)
• Post-mixing automatic subtraction accounts for evaporation since last update
• Original mix_color flow preserved for backward compatibility
• Two new work queues: maintenance (priority 4), monitoring (priority 5)

Operations

# Initialize system (first time or reset)
initialize_inventory(red_volume=15000, yellow_volume=15000, blue_volume=15000)

# Color mixing automatically checks and subtracts
mix_color_with_inventory(R=120, Y=50, B=80, G=0, mix_well="B2")
# Raises: ValueError if stock < (required + 100µL threshold)

# Manual restock with audit trail
restock_inventory(red_volume=10000, yellow_volume=5000)
# Logs operator, timestamp, volumes to MongoDB

CLI

python orchestrator_restock.py check 5.0          # Alert if < 5ml
python orchestrator_restock.py restock 10 5 0 tech_id
python orchestrator_restock.py initialize 15 15 15

All MongoDB connections use try-finally for proper cleanup. Environment variables (MONGODB_PASSWORD, blinded_connection_string) handled gracefully for testing. Mock OT-2 implementation available via USE_REAL_OPENTRONS=false.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Add "restock" maintenance Prefect step for OT2 color matching demo</issue_title>
<issue_description>Likewise, probably time for me to handle stocking more strategically at some point, given that students were running experiments while (EDIT: yellow and red) were out of stock. I can also probably dig up the threads I have related to this. Maybe some issues in this repo, probably also on the self-driving-lab-demo discussions.</issue_description>

<agent_instructions>https://github.com/AccelerationConsortium/ac-dev-lab/blob/main/src/ac_training_lab/ot-2/_scripts/OT2mqtt.py

There would be an extra collection within mongodb I guess, for storing the state. We could assume a certain rate of evaporation and also make sure that with each experiment call, we're subtracting some amount. Likewise, we'd need the ability to trigger this manually.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@Neil-YL Feel free to ask if you cannot find things you need or anything you think I may know.😉

• Fixes Add "restock" maintenance Prefect step for OT2 color matching demo #434

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