DEBUG-3700 UDS HTTP server helper for test suite

[p-datadog]

What does this PR do?

DRY the code to set up a Webrick server listening on a unix domain socket

Motivation:

UDS testing for telemetry (in #4630) + DRY existing test code

Change log entry
None

Additional Notes:

How to test the change?
Existing CI

[datadog-datadog-prod-us1]

Datadog Summary

❌ Code Quality    ✅ Code Security    ✅ Dependencies

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[pr-commenter]

Benchmarks

Benchmark execution time: 2025-05-12 14:14:12

Comparing candidate commit bd8c730 in PR branch uds-http-server-helper with baseline commit deadb14 in branch master.

Found 1 performance improvements and 1 performance regressions! Performance is the same for 29 metrics, 2 unstable metrics.

scenario:profiling - hold / resume

• 🟩 throughput [+89287.430op/s; +93050.113op/s] or [+5.457%; +5.687%]

scenario:tracing - Propagation - Trace Context

• 🟥 throughput [-4055.314op/s; -3944.274op/s] or [-10.848%; -10.551%]

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 94.44444% with 1 line in your changes missing coverage. Please review.

Project coverage is 97.77%. Comparing base (deadb14) to head (7d91eb4).
Report is 534 commits behind head on master.

Files with missing lines	Patch %	Lines
spec/datadog/core/crashtracking/component_spec.rb	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4636      +/-   ##
==========================================
- Coverage   97.77%   97.77%   -0.01%     
==========================================
  Files        1415     1415              
  Lines       86568    86560       -8     
  Branches     4386     4386              
==========================================
- Hits        84644    84632      -12     
- Misses       1924     1928       +4     

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