test: add unexpected disconnect guards to more client test files

[samayer12]

This relates to...

Relates to #251 and #4833.

Rationale

Adds disconnect guard assertions to unit tests that follow the pattern seen in #4833. This PR adds the guard to additional tests that do not already adopt the pattern, and documents it.

Changes

Disconnect guards

This PR structures tests along these lines:

  client.on('disconnect', () => {
    if (!client.closed && !client.destroyed) {
      t.fail('unexpected disconnect')
    }
  })

Fix encoding test (Node 20 + macOS)

I noticed that there were CI issues with test/fetch/encoding.js on Node.js 20 + macOS. As part of this PR, I also changed the chain limit test server from server.listen(0, 'listening') to specify 127.0.0.1 which fixed the test failure's ECONNRESET error. I also added flushHeaders() and per-socket setNoDelay() as seen in #4496.

Features

N/A

Bug Fixes

N/A

Breaking Changes and Deprecations

None

Benchmarks

[bench:run] ┌─────────┬───────────────────────┬─────────┬────────────────────┬────────────┬─────────────────────────┐
[bench:run] │ (index) │ Tests                 │ Samples │ Result             │ Tolerance  │ Difference with slowest │
[bench:run] ├─────────┼───────────────────────┼─────────┼────────────────────┼────────────┼─────────────────────────┤
[bench:run] │ 0       │ 'http - no keepalive' │ 85      │ '4648.39 req/sec'  │ '± 2.91 %' │ '-'                     │
[bench:run] │ 1       │ 'node-fetch'          │ 20      │ '11330.13 req/sec' │ '± 2.88 %' │ '+ 143.74 %'            │
[bench:run] │ 2       │ 'axios'               │ 15      │ '11494.72 req/sec' │ '± 2.82 %' │ '+ 147.28 %'            │
[bench:run] │ 3       │ 'got'                 │ 20      │ '12015.76 req/sec' │ '± 2.92 %' │ '+ 158.49 %'            │
[bench:run] │ 4       │ 'undici - fetch'      │ 40      │ '14663.42 req/sec' │ '± 2.82 %' │ '+ 215.45 %'            │
[bench:run] │ 5       │ 'request'             │ 35      │ '14892.99 req/sec' │ '± 2.82 %' │ '+ 220.39 %'            │
[bench:run] │ 6       │ 'superagent'          │ 15      │ '18511.94 req/sec' │ '± 2.25 %' │ '+ 298.24 %'            │
[bench:run] │ 7       │ 'http - keepalive'    │ 15      │ '19108.18 req/sec' │ '± 2.74 %' │ '+ 311.07 %'            │
[bench:run] │ 8       │ 'undici - pipeline'   │ 55      │ '22599.61 req/sec' │ '± 2.99 %' │ '+ 386.18 %'            │
[bench:run] │ 9       │ 'undici - stream'     │ 30      │ '25741.88 req/sec' │ '± 2.96 %' │ '+ 453.78 %'            │
[bench:run] │ 10      │ 'undici - request'    │ 10      │ '28529.09 req/sec' │ '± 2.17 %' │ '+ 513.74 %'            │
[bench:run] │ 11      │ 'undici - dispatch'   │ 20      │ '29355.94 req/sec' │ '± 2.96 %' │ '+ 531.53 %'            │
[bench:run] └─────────┴───────────────────────┴─────────┴────────────────────┴────────────┴─────────────────────────┘

Status

• I have read and agreed to the Developer's Certificate of Origin
• Tested
• Benchmarked (optional)
• Documented
• Review ready
• In review
• Merge ready

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.01%. Comparing base (b12081c) to head (ba79c89).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4844      +/-   ##
==========================================
- Coverage   93.02%   93.01%   -0.02%     
==========================================
  Files         112      112              
  Lines       35157    35157              
==========================================
- Hits        32705    32701       -4     
- Misses       2452     2456       +4     

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[metcoder95]

why the loopback change?