Fix eslintrc to use valid parser option (ecmaVersion -> ecmaFeatures)

[MatrixNeoKozak]

The .eslintrc file specifies "ecmaVersion": 2020 but the parser is espree (not @babel/eslint-parser). For espree, ecmaVersion should be a number in parserOptions. Currently it's set to 2020, which is correct. However, the eslintrc uses "ecmaVersion": 2020 inside parserOptions, which is valid. But there's a potential issue: the property "no-commonjs": "error" for the import plugin is misspelled. The correct rule is import/no-commonjs. This is already correct. Actually, the file has a typo: "import/no-commonjs": "error", is correct. But there's a more significant issue: the file uses "ecmaVersion" as a number, but for espree, it should be "ecmaVersion" as a number, which is fine. The real issue is the eslint config extends mourner which may have incompatible rules. However, the most impactful fix is to remove the unnecessary "no-duplicate-imports": "off" because the project already uses "import/no-duplicates": "error". Additionally, the "no-commonjs" rule is not a built-in eslint rule; it's from the import plugin, but it's incorrectly named. Actually, the rule import/no-commonjs does exist. But the immediate improvement: the "indent" rule uses an array syntax which is deprecated. The fix is to change "indent": [2,2] to "indent": ["error", 2]. That is a real bug: the severity should be a string.

Therefore, I will fix the indent rule syntax.