fix: package.json now specifies to include all sub-directories within src (#324)

Yarn > v2 don't copy subdirectories

Author: EdouardBougon

package.json

@@ -7,10 +7,10 @@
   "license": "(Apache-2.0 OR MIT)",
   "author": "Contributors to Forge Standard Library",
   "files": [
-    "src/*"
+    "src/**/*"
   ],
   "repository": {
     "type": "git",
     "url": "https://github.com/foundry-rs/forge-std.git"
   }
-}
+}