[CODE HEALTH] fix nondeterministic pointer iteration order warnings

[dbarker]

Contributes to #2053

Changes

• clean up memory management of the otlp utils functions
  • OtlpRecordableUtils::PopulateRequest takes in recordables through a const ref nostd::span. Before the method took ownership of the recordables and destroyed them which is unexpected. This PR keeps ownership with the caller.
  • The OTLP proto messages owned by the recordables are not created in a protobuf Arena but the request message is. This results in a deep copy when trying to move the recordable's Span/LogRecord into the request. This PR changes to an explicit deep copy for clarity.
  • Update the PopulateRequest methods to remove local temporary proto messages and only create/modify the request message Arena allocated sub messages directly.
• add tests to cover corner cases
• fix the following warnings:

---

File	Line	Message
opentelemetry-cpp/exporters/otlp/src/otlp_recordable_utils.cc	86	iteration of pointers is nondeterministic
opentelemetry-cpp/exporters/otlp/src/otlp_recordable_utils.cc	151	iteration of pointers is nondeterministic

---

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[codecov]

Codecov Report

❌ Patch coverage is 98.03922% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 82.09%. Comparing base (d87c130) to head (fcda002).

Files with missing lines	Patch %	Lines
exporters/otlp/src/otlp_recordable_utils.cc	98.04%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4035      +/-   ##
==========================================
+ Coverage   82.06%   82.09%   +0.04%     
==========================================
  Files         385      385              
  Lines       15891    15891              
==========================================
+ Hits        13039    13044       +5     
+ Misses       2852     2847       -5     

Files with missing lines	Coverage Δ
exporters/otlp/src/otlp_recordable_utils.cc	98.39% <98.04%> (+4.64%)	⬆️

... and 3 files with indirect coverage changes

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