chore(deps): migrate from tsup to tsdown (#315)

Author: ocavue

package.json

@@ -62,7 +62,7 @@
     "prosemirror-menu": "^1.2.4",
     "prosemirror-schema-basic": "^1.2.4",
     "prosemirror-test-builder": "^1.1.1",
-    "tsup": "^8.4.0",
+    "tsdown": "^0.16.8",
     "typescript": "^5.7.3",
     "vite": "^6.2.6",
     "vitest": "^3.1.1"
@@ -72,8 +72,8 @@
     "build_demo": "vite build demo",
     "typecheck": "tsc --noEmit",
     "test": "vitest",
-    "build": "tsup",
-    "watch": "tsup --watch",
+    "build": "tsdown",
+    "watch": "tsdown --watch",
     "build_readme": "builddocs --name tables --format markdown --main src/README.md src/*.js > README.md",
     "format": "prettier --write .",
     "lint": "eslint ./src/ ./test/ && prettier --check .",