chore(*): build system improvements

* use tsdown cli/configuration scheme instead of internal options
* make tsdown plugins individually addressable
* adds a barrel-dts plugin to fix some compatibility issues with commonjs dependants
* changes build scripts in each package

Fixes #9252
Fixes #9268

Author: hntrl

.changeset/config.json

@@ -17,7 +17,9 @@
   "baseBranch": "main",
   "updateInternalDependencies": "patch",
   "ignore": [
-    "examples"
+    "examples",
+    "@langchain/build",
+    "@langchain/eslint"
   ],
   "___experimentalUnsafeOptions_WILL_CHANGE_IN_PATCH": {
     "onlyUpdatePeerDependentsWhenOutOfRange": true