Add option to override span events serialization

[marcotc]

For agent-less setups, when native support is desired (e.g. the downstream agent supports native span events), this PR adds an option to override the agent decision and send native span events regardless of the environment.

Change log entry
Yes. Add an option to override span events serialization for agent-less environments.

How to test the change?
There are unit tests, and this change will allow to better coverage in parametric tests.

[datadog-datadog-prod-us1]

Datadog Report

Branch report: ruby-option-span-events
Commit report: 43805f5
Test service: dd-trace-rb

✅ 0 Failed, 20663 Passed, 1371 Skipped, 3m 10.93s Total Time

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-03-19 00:43:30

Comparing candidate commit 43805f5 in PR branch ruby-option-span-events with baseline commit 7d88b81 in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 31 metrics, 2 unstable metrics.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.70%. Comparing base (7d88b81) to head (43805f5).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4507      +/-   ##
==========================================
- Coverage   97.70%   97.70%   -0.01%     
==========================================
  Files        1381     1381              
  Lines       83973    84106     +133     
  Branches     4251     4253       +2     
==========================================
+ Hits        82043    82172     +129     
- Misses       1930     1934       +4     

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[ivoanjo]

👍 LGTM

[maycmlee]

A small suggestion and question.

[maycmlee]

@marcotc thanks for the explanation! just a small suggestion, but going to approve to not block this.