refactor(npm): experiment with exports.default option

This change may mean that the package works as expected under more environments.
Further testing is being ensured to ensure this does not cause regressions.

package.json

@@ -21,18 +21,21 @@
     ".": {
       "types": "./build/esm5/entry/index.d.mts",
       "import": "./build/esm5/entry/index.mjs",
+      "default": "./build/esm5/entry/index.mjs",
       "node": "./build/esm5/entry/index.mjs",
       "bun": "./src/index.mts"
     },
     "./contrib/transient-ref": {
       "types": "./build/esm5/contrib/transient-ref/index.d.mts",
       "import": "./build/esm5/contrib/transient-ref/index.mjs",
+      "default": "./build/esm5/contrib/transient-ref/index.mjs",
       "node": "./build/esm5/contrib/transient-ref/index.mjs",
       "bun": "./src/contrib/transient-ref/index.mts"
     },
     "./contrib/util/synchronous-disposable": {
       "types": "./build/esm5/contrib/util/synchronous-disposable.d.mts",
       "import": "./build/esm5/contrib/util/synchronous-disposable.mjs",
+      "default": "./build/esm5/contrib/util/synchronous-disposable.mjs",
       "node": "./build/esm5/contrib/util/synchronous-disposable.mjs",
       "bun": "./src/contrib/util/synchronous-disposable.class.mts"
     }