Migrate the internal parsing library to mdom and add more coverage

jest.config.js

@@ -7,6 +7,10 @@ export default {
   testPathIgnorePatterns: ['/node_modules/', '/cli/'],
   moduleNameMapper: {
     '@/(.*)': '<rootDir>/src/$1',
+    // @stringsync/mdom only exposes an ESM "import" export condition, which jest's CJS resolver can't follow. Point the
+    // bare specifier at its dist entry and let babel transform it (see transformIgnorePatterns).
+    '^@stringsync/mdom$': '<rootDir>/node_modules/@stringsync/mdom/dist/index.js',
   },
+  transformIgnorePatterns: ['/node_modules/(?!(@stringsync/mdom)/)'],
   reporters: ['default', 'jest-image-snapshot/src/outdated-snapshot-reporter.js'],
 };

package.json

@@ -25,6 +25,7 @@
   "license": "MIT",
   "scripts": {},
   "dependencies": {
+    "@stringsync/mdom": "^0.1.0",
     "jszip": "3.10.1",
     "vexflow": "5.0.0"
   },

src/parsing/index.ts

@@ -1,2 +1,5 @@
-export * from './mxl';
-export * from './musicxml';
+// Production parsing is powered by the mdom adapter (@stringsync/mdom). The class names are kept for API compatibility:
+// `MusicXMLParser`/`MXLParser` still parse MusicXML/MXL, now by reading mdom instead of the @/musicxml DOM wrappers.
+// The legacy readers remain importable from '@/parsing/musicxml' and '@/parsing/mxl' for the IR-equivalence test.
+export { MdomParser as MusicXMLParser, type MdomParserOptions as MusicXMLParserOptions } from './mdom';
+export { MdomMXLParser as MXLParser, type MdomMXLParserOptions as MXLParserOptions } from './mdom';