Adds base class for ContentService performance benchmarks with:
- RecordBenchmark() for timing capture
- MeasureAndRecord() with warmup support for non-destructive ops
- MeasureAndRecord<T>() with warmup for read-only ops returning values
- JSON output wrapped in [BENCHMARK_JSON] markers for extraction
- skipWarmup parameter for destructive operations
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Co-Authored-By: Claude <noreply@anthropic.com>
