feat(bigquery-jdbc): add aggregation logic

[Neenu1995]

• In-Memory Metric Aggregation (TelemetryBatcher):

  • Added raw event queue (LinkedBlockingQueue) with dedicated in-memory aggregation maps using composite keys (ConnectionAttemptKey, StatementExecutionKey, ErrorMetricKey, FeatureUsageKey).
  • Aggregates event frequencies and latency histograms (sum, total count, and bucket distributions) directly upon ingestion, significantly reducing memory footprint and object allocations.
  • Implemented atomic map swapping on flush with merge-back capabilities (requeue) on transport failures.

• Streamlined Recording Pipeline (TelemetryManager):

  • Updated recordConnectionAttempt, recordStatementExecution, and recordFeatureUsage to pass raw parameters directly to TelemetryBatcher without allocating intermediate Protobuf messages.
  • Added calculateBucketIndex to compute latency histogram bucket indexes directly during statement recording.

[gemini-code-assist]

Code Review

This pull request refactors the telemetry batching mechanism in TelemetryBatcher and TelemetryManager to use lock-free, in-memory accumulators (ConcurrentHashMap and LongAdder) instead of a blocking queue of Protobuf messages. This optimization eliminates object allocation and GC overhead during telemetry recording. The reviewer identified a potential issue in the refactored reschedule method, which is missing an isClosed guard, potentially leading to a RejectedExecutionException or scheduling tasks on a closed batcher during shutdown.