Add Vitest test command and run unit tests

[devin-ai-integration]

Add Vitest test command and run unit tests

Summary

This PR adds a proper test runner setup using Vitest for the PVM Debugger project. Previously, the project had unit tests in src/packages/pvm/jam-codec/ but no npm script to run them.

Changes:

• Added Vitest as dev dependency in package.json
• Added npm run test and npm run test:watch scripts
• Created vitest.config.ts to run unit tests under src/ while excluding Playwright E2E tests in tests/
• Migrated 2 existing unit test files from node:test imports to vitest imports
• Updated package-lock.json with new dependencies

The unit tests now run via npm run test and all 31 tests pass (2 test files covering JAM codec functionality).

Review & Testing Checklist for Human

• Run npm run test locally - Verify it executes and all tests pass (should show 2 files, 31 tests)
• Check test migration correctness - Compare test behavior before/after by reviewing the migrated test files for any unintended changes beyond import statements
• Verify Playwright E2E tests still work - Run existing E2E test commands to ensure vitest config exclusion doesn't interfere
• Test the test:watch script - Run npm run test:watch to ensure watch mode works correctly

Recommended test plan:

1. Clean install: rm -rf node_modules package-lock.json && npm install
2. Run unit tests: npm run test (expect 31 passing tests)
3. Run lint: npm run lint (should pass)
4. Verify E2E tests independently (if you have commands for those)

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Diagram

%%{ init : { "theme" : "default" }}%%
flowchart TD
    PJ["package.json<br/>Scripts + Dependencies"]:::major-edit
    VC["vitest.config.ts<br/>Test Configuration"]:::major-edit
    T1["src/packages/pvm/jam-codec/<br/>little-endian-decoder.test.ts"]:::minor-edit
    T2["src/packages/pvm/jam-codec/<br/>decode-natural-number.test.ts"]:::minor-edit
    E2E["tests/<br/>Playwright E2E Tests"]:::context
    
    PJ -->|"defines test scripts"| VC
    VC -->|"includes"| T1
    VC -->|"includes"| T2
    VC -->|"excludes"| E2E
    
    subgraph Legend
        L1[Major Edit]:::major-edit
        L2[Minor Edit]:::minor-edit
        L3[Context/No Edit]:::context
    end
    
    classDef major-edit fill:#90EE90
    classDef minor-edit fill:#87CEEB  
    classDef context fill:#FFFFFF

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Notes

Link to Devin run: https://app.devin.ai/sessions/32696a16f4d549ffbd30d1b02a60040c

Requested by: Tomek (@tomusdrw)

The migration from node:test to vitest was minimal - only import statements changed, not test logic. However, different test runners can have subtle behavioral differences, so human verification is recommended. The vitest config intentionally separates unit tests (src/) from E2E tests (tests/) to avoid conflicts.

[devin-ai-integration]

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