Improves all-day event layout calculation

Refactors all-day event rendering to use a layout engine
for overlap detection and positioning, ensuring events
are placed in available rows and columns.

Removes deprecated method and adds unit tests.

package.json

@@ -7,13 +7,20 @@
     "build": "node build.js",
     "build-simple": "esbuild src/**/*.ts --outdir=js --format=esm --sourcemap=inline --target=es2020",
     "watch": "esbuild src/**/*.ts --outdir=js --format=esm --sourcemap=inline --target=es2020 --watch",
-    "clean": "powershell -Command \"if (Test-Path js) { Remove-Item -Recurse -Force js }\""
+    "clean": "powershell -Command \"if (Test-Path js) { Remove-Item -Recurse -Force js }\"",
+    "test": "vitest",
+    "test:run": "vitest run",
+    "test:ui": "vitest --ui"
   },
   "devDependencies": {
+    "@vitest/ui": "^3.2.4",
     "esbuild": "^0.19.0",
-    "typescript": "^5.0.0"
+    "jsdom": "^27.0.0",
+    "typescript": "^5.0.0",
+    "vitest": "^3.2.4"
   },
   "dependencies": {
+    "@rollup/rollup-win32-x64-msvc": "^4.52.2",
     "fuse.js": "^7.1.0"
   }
 }