🔧 Replace Vite/Vitest with TypeScript 7 and node --test

- Use tsc 7 for build (vite no longer needed for a Node library)
- Use node --test with --experimental-strip-types for tests (vitest dropped)
- Use c8 for coverage instead of vitest's built-in coverage
- Add tsconfig.build.json separating typecheck from emit config
- Drop DOM lib, add strict noUncheckedIndexedAccess/noImplicitOverride
- Pin engines.node to >=22.6 (required for --experimental-strip-types)
- Update CI to Node 24 LTS (unflagged strip-types)
- Add @types/node for node:test / node:assert types

tsconfig.build.json

@@ -0,0 +1,9 @@
+{
+    "extends": "./tsconfig.json",
+    "compilerOptions": {
+        "noEmit": false,
+        "rootDir": "src",
+        "outDir": "dist"
+    },
+    "exclude": ["src/**/*.test.ts", "src/**/__tests__/**"]
+}