feat: add resend attribute to span tracing

[ldetmer]

This adds attribute for HTTP_REQUEST_RESEND_COUNT to span tracing. This only gets populated in case of a retry on the client side.

no resend attribute on first attempt
example retry 1
example retry 4

[gemini-code-assist]

Summary of Changes

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This pull request enhances the BigQuery client's OpenTelemetry tracing capabilities by incorporating retry attempt information directly into the generated spans. This provides valuable context for debugging and analyzing the behavior of requests that undergo retries, allowing developers to quickly identify and understand the impact of transient errors and retry logic on overall request latency and success rates.

Highlights

• Tracing Retry Attempts: Introduced a mechanism to track and record the number of retry attempts for HTTP requests within OpenTelemetry spans. This is achieved by storing the current attempt count in a ThreadLocal variable in BigQueryRetryAlgorithm.
• OpenTelemetry Span Attribute: Modified HttpTracingRequestInitializer to read the retry attempt count from the ThreadLocal and add it as an HTTP_REQUEST_RESEND_COUNT attribute to the OpenTelemetry span if the attempt count is greater than zero.
• Comprehensive Testing: Added new unit tests in HttpBigQueryRpcTest and HttpTracingRequestInitializerTest to ensure the HTTP_REQUEST_RESEND_COUNT attribute is correctly set on spans during retries and is not set when tracing is disabled or no retry has occurred.

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[gemini-code-assist]

Code Review

This pull request introduces OpenTelemetry tracing for BigQuery retry attempts. It adds a ThreadLocal variable to BigQueryRetryAlgorithm to store the current retry count, which is then used by HttpTracingRequestInitializer to add an HTTP_REQUEST_RESEND_COUNT attribute to the HTTP request span. New tests have been added to validate this functionality. Feedback includes a high-severity concern regarding potential ThreadLocal leakage that could lead to incorrect telemetry data, with a suggestion to reset the ThreadLocal after use. Additionally, a medium-severity design concern was raised about exposing ThreadLocal as a public static final field, which is considered an anti-pattern and creates tight coupling, though it's accepted for now due to current framework constraints.

[gemini-code-assist]

Exposing a ThreadLocal as a public static final field is generally considered an anti-pattern as it creates a hidden, global-like dependency between components and can be prone to misuse. While it seems necessary here to communicate the retry state to HttpTracingRequestInitializer due to framework constraints, it would be ideal to find a way to pass this context explicitly if possible in the future. For now, this is acceptable, but please be mindful of the tight coupling it introduces.

[ldetmer]

added helper methods, but note this isn't something we have easy access too, as retry logic is handled inside of apiary client, so we do have to expose it somehow to the interceptor.