feat(mock): add support reply option callbacks

[suneettipirneni]

This PR is similar to #1200, except it allows dynamic mocking of all reply options rather than just the data.

mockPool.intercept({
  path: '/echo',
  method: 'GET',
  headers: {
    'User-Agent': 'undici',
    Host: 'example.com'
  }
}).reply(({ headers }) => ({ statusCode: 200, data: { message: headers.get('message') }})))

const { statusCode, body, headers } = await request('http://localhost:3000', {
  headers: {
    message: 'hello world!'
  }
})

console.log('response received', statusCode) // response received 200
console.log('headers', headers) // { 'content-type': 'application/json' }

for await (const data of body) {
  console.log('data', data.toString('utf8')) // { "message":"hello world!" }
}

This is useful in situations where the status code and the response headers need to be dynamically mocked.

[codecov-commenter]

Codecov Report

Merging #1211 (3620ca1) into main (d94dc15) will increase coverage by 0.05%.
The diff coverage is 100.00%.

❗ Current head 3620ca1 differs from pull request most recent head db09c2d. Consider uploading reports for the commit db09c2d to get more accurate results

@@            Coverage Diff             @@
##             main    #1211      +/-   ##
==========================================
+ Coverage   93.38%   93.43%   +0.05%     
==========================================
  Files          43       43              
  Lines        4035     4052      +17     
==========================================
+ Hits         3768     3786      +18     
+ Misses        267      266       -1     

Impacted Files	Coverage Δ
lib/mock/mock-interceptor.js	100.00% <100.00%> (ø)
lib/mock/mock-utils.js	100.00% <100.00%> (ø)
lib/fetch/request.js	82.57% <0.00%> (+0.41%)	⬆️

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[mcollina]

lgtm