* fix: prefer .pnpmfile.mjs by default
* fix: handle ERR_MODULE_NOT_FOUND for missing optional .pnpmfile.mjs
Node's dynamic import() throws ERR_MODULE_NOT_FOUND (not MODULE_NOT_FOUND
like require()) when a file doesn't exist. This caused a hard error when
tryLoadDefaultPnpmfile was enabled and .pnpmfile.mjs was absent.
* fix: load only .pnpmfile.mjs when it exists, not both .mjs and .cjs
When both .pnpmfile.mjs and .pnpmfile.cjs exist, only the .mjs file
is now loaded. Previously both were loaded and their hooks combined.
Also adds .mjs support for config dependency plugins.