feat: add subtract operation for number state variables

[leowla]

Issue

Users expect a subtract operation when "add" exists and sometimes confuse "set" for "add".

Solution

Add a subtract option

Risk

Low

Checklist

• Acceptance criteria met
• Wiki documentation is written and up to date
• Continuous integration build passing

Summary by CodeRabbit

• New Features
  • Added subtraction operations for numeric state variables.
  • Numeric values can now be decreased by a specified amount.
  • Existing set and add operations remain available; string and boolean behavior is unchanged.

[linear]

VPS-145

[coderabbitai]

📝 Walkthrough

Walkthrough

Backend and frontend state variable modules add a SUBTRACT operation, permit it for numeric state variables, and decrement matching values during operation application.

Changes

Numeric State Subtraction

Layer / File(s)	Summary
Operation contracts backend/src/util/statevariables/stateTypes.js, frontend/src/components/StateVariables/stateTypes.js	Adds SUBTRACT and permits it for NUMBER state variables while leaving string and boolean operations unchanged.
Subtraction execution backend/src/util/statevariables/stateOperations.js, frontend/src/components/StateVariables/stateOperations.js	Applies subtraction by decrementing the matched state variable’s current value.

Estimated code review effort: 2 (Simple) | ~5 minutes

Suggested reviewers: harbassan, hazikchaudhry

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly states the main change: adding a subtract operation for number state variables.
Description check	✅ Passed	The description covers Issue, Solution, Risk, and most of the checklist, but omits unit and integration test items.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch vps-145-subtract-operation-for-state-variables

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[harbassan]

easy enough