Add response token count logic to OpenAI instrumentation.

[umaannamalai]

This PR updates OpenAI instrumentation and tests to pull token counts directly from the response object. If a customer has an LLM token counting callback function registered, this will still take priority over the response token count values.

It also removes token count calculations from error cases as the agent will consistently stop reporting token counts when a error was met during the creation of an embedding or chat completion.

[github-actions]

✅MegaLinter analysis: Success

Descriptor	Linter	Files	Fixed	Errors	Warnings	Elapsed time
✅ ACTION	actionlint	7		0	0	1.04s
✅ MARKDOWN	markdownlint	7	0	0	0	1.48s
✅ PYTHON	ruff	946	0	0	0	1.03s
✅ PYTHON	ruff-format	946	1	0	0	0.42s
✅ YAML	prettier	15	0	0	0	1.53s
✅ YAML	v8r	15		0	0	6.23s
✅ YAML	yamllint	15		0	0	0.66s

See detailed reports in MegaLinter artifacts

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.61%. Comparing base (b1408de) to head (ddbcb36).

❗ There is a different number of reports uploaded between BASE (b1408de) and HEAD (ddbcb36). Click for more details.

HEAD has 2 uploads less than BASE

Flag	BASE (b1408de)	HEAD (ddbcb36)
	3	1

Additional details and impacted files

@@                     Coverage Diff                      @@
##           feature-llm-token-counts    #1498      +/-   ##
============================================================
- Coverage                     81.48%   73.61%   -7.87%     
============================================================
  Files                           209      209              
  Lines                         23815    23841      +26     
  Branches                       3753     3757       +4     
============================================================
- Hits                          19406    17551    -1855     
- Misses                         3153     5154    +2001     
+ Partials                       1256     1136     -120     

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