Include test files in TypeScript type checking

Add test/**/*.mts to tsconfig.json includes to ensure test utilities
and test files are type-checked by pnpm run check:tsc

Author: jdalton

tsconfig.json

@@ -1,5 +1,5 @@
 {
   "extends": "./.config/tsconfig.base.json",
-  "include": ["src/**/*.mts", "*.config.mts"],
+  "include": ["src/**/*.mts", "test/**/*.mts", "*.config.mts"],
   "exclude": ["src/**/*.test.mts"]
 }