feat: support ArrowFunctionExpression

[AriPerkkio]

🔗 Linked issue

• Fixes Missing castings #37
• There has already been another linked PR to Missing castings #37 that implemented the missing identifiers. This PR closes that issue completely.

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Adds support for traversing ArrowFunctionExpressions. This is needed for vitest-dev/vitest#4695.

I've verified that with these changes following test will pass and covers my use case:

it("Vitest threshold updating", () => {
  const mod = parseModule(`
    import { defineConfig } from 'vitest/config'

    export default defineConfig((config) => ({
      test: {
        coverage: {
          thresholds: {
            autoUpdate: true,
            lines: 50,
            branches: 1,
          }
        }
      }
     }))
  `);

  mod.exports.default.$args[0].$body.test.coverage.thresholds.lines = 95;
  mod.exports.default.$args[0].$body.test.coverage.thresholds.branches = 100;

  expect(mod.generate().code).toMatchInlineSnapshot(`
      "import { defineConfig } from 'vitest/config'

      export default defineConfig((config) => ({
        test: {
          coverage: {
            thresholds: {
              autoUpdate: true,
              lines: 95,
              branches: 100,
            }
          }
        }
       }))"
    `);
});

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (f9b707f) 93.53% compared to head (5e5a09f) 93.58%.

Files	Patch %	Lines
src/proxy/arrow-function-expression.ts	93.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #98      +/-   ##
==========================================
+ Coverage   93.53%   93.58%   +0.04%     
==========================================
  Files          23       24       +1     
  Lines        1749     1792      +43     
  Branches      328      331       +3     
==========================================
+ Hits         1636     1677      +41     
- Misses        113      115       +2     

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[AriPerkkio]

5e5a09f is related to esno's dependency on tsx and this error that comes up now with newer versions of Node: privatenumber/tsx#421