feat: enhance type assertions in level1-assertions and update tsconfig for vitest

[esgn]

This pull request focuses on improving the robustness of test assertions and simplifying the test configuration. The most notable changes are enhanced type checking in test helper functions and a minor update to the TypeScript test configuration.

Test assertion improvements:

• Added explicit array type checks in expectNonEmptyResults and expectFeatureCollectionWithFeatures to throw clear errors if the expected arrays are missing or of the wrong type, improving reliability and debuggability of tests.

Test configuration update:

• Updated tsconfig.test.json to use the "vitest" type instead of "vitest/globals" and removed the unnecessary inclusion of the src directory from the test build, streamlining the test setup.