DEBUG-3568 DRY transport options, remove HTTP.new method

[p-datadog]

What does this PR do?

Reduces duplication of existing transport code by removing the HTTP.new method which was identical for all transports and removing the code that copied agent settings into transport options.

Transport options are now explicitly enumerated (they are api_version and headers) instead of being a hash. This will make code that passed invalid or unknown options fail instead of silently doing nothing.

Motivation:
Preparation for chunking of dynamic instrumentation event submissions

Change log entry
None

Additional Notes:
This PR should not contain any API changes. The options style arguments have been replaced with explicit keyword arguments in some methods but the set of arguments accepted remains the same as before.

How to test the change?
Existing unit tests

[datadog-datadog-prod-us1]

Datadog Report

Branch report: transport-options
Commit report: f0ab44b
Test service: dd-trace-rb

✅ 0 Failed, 20523 Passed, 1372 Skipped, 3m 23.28s Total Time

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-03-19 15:13:10

Comparing candidate commit f0ab44b in PR branch transport-options with baseline commit b27ad8d in branch master.

Found 3 performance improvements and 0 performance regressions! Performance is the same for 28 metrics, 2 unstable metrics.

scenario:line instrumentation - targeted

• 🟩 throughput [+14324.598op/s; +14856.545op/s] or [+9.265%; +9.609%]

scenario:line instrumentation - untargeted

• 🟩 throughput [+4716.251op/s; +4974.279op/s] or [+5.218%; +5.503%]

scenario:method instrumentation

• 🟩 throughput [+10282.473op/s; +10745.927op/s] or [+6.125%; +6.402%]

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.73%. Comparing base (b27ad8d) to head (f0ab44b).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4469   +/-   ##
=======================================
  Coverage   97.72%   97.73%           
=======================================
  Files        1385     1386    +1     
  Lines       84228    84159   -69     
  Branches     4281     4256   -25     
=======================================
- Hits        82315    82255   -60     
+ Misses       1913     1904    -9     

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