refactor: small improvements

[ilteoood]

PR to introduce small improvements, like reading the url.length just once and avoid invoking a function to retrieve the encoding extension.

Checklist

• run npm run test && npm run benchmark --if-present
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[Uzlopak]

I did not test my suggestions...

[ilteoood]

I had to remove the || '' fallback, otherwise a test was failing

[Uzlopak]

which test would have failed when doing || '' ?

[ilteoood]

which test would have failed when doing || '' ?
Here is the log:

✖ failing tests:

test at test/static.test.js:2684:1
✖ will serve uncompressed files if there are no compressed variants on disk (2.138959ms)
 AssertionError [ERR_ASSERTION]: Expected values to be strictly deep-equal:
 + actual - expected
 
 + 'deflate'
 - undefined
     at assert.<computed> [as deepStrictEqual] (node:internal/test_runner/test:242:18)
     at TestContext.<anonymous> (/Users/ilteoood/Documents/git/fastify/fastify-static/test/static.test.js:2707:14)
     at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
     at async Test.run (node:internal/test_runner/test:797:9)
     at async Test.processPendingSubtests (node:internal/test_runner/test:526:7) {
   generatedMessage: true,
   code: 'ERR_ASSERTION',
   actual: 'deflate',
   expected: undefined,
   operator: 'deepStrictEqual'
 }

test at test/static.test.js:2833:1
✖ will serve uncompressed files if there are no compressed variants on disk (with wildcard: false) (2.539583ms)
 AssertionError [ERR_ASSERTION]: Expected values to be strictly deep-equal:
 + actual - expected
 
 + 'deflate'
 - undefined
     at assert.<computed> [as deepStrictEqual] (node:internal/test_runner/test:242:18)
     at TestContext.<anonymous> (/Users/ilteoood/Documents/git/fastify/fastify-static/test/static.test.js:2857:14)
     at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
     at async Test.run (node:internal/test_runner/test:797:9)
     at async Test.processPendingSubtests (node:internal/test_runner/test:526:7) {
   generatedMessage: true,
   code: 'ERR_ASSERTION',
   actual: 'deflate',
   expected: undefined,
   operator: 'deepStrictEqual'
 }

[Copilot]

Pull Request Overview

This PR introduces small performance and code quality improvements to the fastify-static plugin, including optimizing property access patterns and replacing function calls with direct object lookups.

• Replaced multiple conditional assignments with nullish coalescing operators for cleaner code
• Optimized encoding extension lookup by replacing function calls with direct object mapping
• Improved loop performance by caching url.length in a variable

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}