test: add test case for SurveyEngine.submitAnswer error condition

[alfieprojectsdev]

This PR adds a test case to field-logic/src/lib/engine.test.ts to verify that SurveyEngine.submitAnswer throws a "Survey not active" error when called before the survey has started (i.e., when currentNodeId is null). This ensures that the precondition for submitting an answer is properly enforced.

Changes:

• Added a test case should throw error if submitAnswer called before start to field-logic/src/lib/engine.test.ts.
• Formatted field-logic/src/lib/engine.test.ts using Prettier.

Verification:

• Ran npx vitest run src/lib/engine.test.ts and all tests passed.
• Ran npx vitest run to ensure no regressions in other tests.

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PR created automatically by Jules for task 2802991447513769445 started by @alfieprojectsdev

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