feat(OpenTelemetry): add per-HTTP request counter metric

[evansims]

Description

Added:

• Adds a per-HTTP request counter metric, fga-client.request. It is disabled by default.

Changed:

• Method signature on credentialsRequest now uses 1 as the default parameter value.
• Changed default unit type in TelemetryCounter/TelemetryCounters. It mistakenly used milliseconds as the default unit type for counters previously.
• Refactored TelemetryHistogram/TelemetryHistograms to use the shared default milliseconds unit type; not necessary to define it each time.

Fixed:

• Moved fromRequest step above exception handling in the synchronous API Client to ensure those attributes were properly collected there. This was already the case in the asynchronous API client.
• Moved http.request.resend_count increment to the top of the retry loop for the synchronous API client to ensure the proper value is collected when an API exception is raised.

References

Closes #130

Review Checklist

• I have clicked on "allow edits by maintainers".
• I have added documentation for new/changed functionality in this PR or in a PR to openfga.dev [Provide a link to any relevant PRs in the references section above]
• The correct base branch is being used, if not main
• I have added tests to validate that the change in functionality is working as expected

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 76.66667% with 7 lines in your changes missing coverage. Please review.

Project coverage is 69.17%. Comparing base (a00f039) to head (916442d).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
openfga_sdk/telemetry/configuration.py	55.55%	4 Missing ⚠️
openfga_sdk/telemetry/metrics.py	57.14%	3 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@ ## main #135 +/- ## ========================================== + Coverage 69.15% 69.17% +0.01%  ========================================== Files 122 122 Lines 9746 9771 +25 ========================================== + Hits 6740 6759 +19  - Misses 3006 3012 +6 

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