feat: add tests and assert coverage (#71)

### Explanation

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### Issue

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### Attestations

- [ ] I have read and agree to the [Code of Conduct](https://docs.nhcarrigan.com/community/coc/)
- [ ] I have read and agree to the [Community Guidelines](https://docs.nhcarrigan.com/community/guide/).
- [ ] My contribution complies with the [Contributor Covenant](https://docs.nhcarrigan.com/dev/covenant/).

### Dependencies

- [ ] I have pinned the dependencies to a specific patch version.

### Style

- [ ] I have run the linter and resolved any errors.
- [ ] My pull request uses an appropriate title, matching the conventional commit standards.
- [ ] My scope of feat/fix/chore/etc. correctly matches the nature of changes in my pull request.

### Tests

- [ ] My contribution adds new code, and I have added tests to cover it.
- [ ] My contribution modifies existing code, and I have updated the tests to reflect these changes.
- [ ] All new and existing tests pass locally with my changes.
- [ ] Code coverage remains at or above the configured threshold.

### Documentation

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### Versioning

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Co-authored-by: Hikari <hikari@nhcarrigan.com>
Reviewed-on: #71
Co-authored-by: Naomi Carrigan <commits@nhcarrigan.com>
Co-committed-by: Naomi Carrigan <commits@nhcarrigan.com>

package.json

@@ -16,6 +16,10 @@
     "test": "vitest run",
     "test:watch": "vitest",
     "test:coverage": "vitest run --coverage",
+    "test:backend": "cd src-tauri && cargo test",
+    "test:backend:coverage": "cd src-tauri && cargo llvm-cov --text",
+    "test:all": "pnpm test && pnpm test:backend",
+    "coverage:all": "pnpm test:coverage && pnpm test:backend:coverage",
     "lint": "eslint .",
     "lint:fix": "eslint . --fix",
     "format": "prettier --write .",
@@ -44,6 +48,7 @@
     "@tauri-apps/cli": "^2",
     "@testing-library/jest-dom": "^6.9.1",
     "@testing-library/svelte": "^5.3.1",
+    "@vitest/coverage-v8": "^4.0.18",
     "eslint": "^9.39.2",
     "eslint-config-prettier": "^10.1.8",
     "eslint-plugin-svelte": "^3.14.0",