fix: ESLint 10 compatibility — drop @babel/eslint-parser, expand peerDeps

[RoiEf]

Fixes #44

Problem

@babel/eslint-parser requires eslint@^7||^8||^9 and crashes on ESLint 10
(scopeManager.addGlobals is not a function) because ESLint 10 ships a new
eslint-scope@9.x API that the Babel parser doesn't support.

Solution

The code already had a TODO to remove the custom parser once class properties
became native — they have been, since ES2022. This PR acts on that TODO:

• index.js — Drop @babel/eslint-parser and all Babel config. Use
  ESLint's built-in espree parser at ecmaVersion: 'latest', which handles
  class properties natively. Move ecmaVersion/sourceType to the correct
  languageOptions level for flat config.
• package.json — Remove @babel/core, @babel/eslint-parser,
  @babel/plugin-syntax-class-properties, @babel/plugin-syntax-jsx.
  Extend peerDependencies to ^8.57.1 || ^9.0.0 || ^10.0.0.
• test/index.test.mjs — Strip volatile fields (nodeType, endLine,
  endColumn) from snapshots so the same snapshot file works under ESLint
  8, 9, and 10.
• .github/workflows/nodejs.yml — Add ESLint 9 and 10 to the CI matrix.
• README.md — Note ESLint 10 flat-config requirement and label the
  setup snippet as compatible with ESLint 8, 9, or 10.

Testing

• All 8 tests pass locally against ESLint 9 (the devDependency version)
• CI matrix now covers ESLint 8, 9, 10, and local

Fixes #44