Add GitHub Actions workflow, baseline results, and documentation for performance benchmarks

Co-authored-by: adamhathcock <527620+adamhathcock@users.noreply.github.com>

tests/SharpCompress.Performance/README.md

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+# SharpCompress Performance Benchmarks
+
+This project contains performance benchmarks for SharpCompress using [BenchmarkDotNet](https://benchmarkdotnet.org/).
+
+## Overview
+
+The benchmarks test all major archive formats supported by SharpCompress:
+- **Zip**: Read (Archive & Reader API) and Write operations
+- **Tar**: Read (Archive & Reader API) and Write operations, including Tar.GZip
+- **Rar**: Read operations (Archive & Reader API)
+- **7Zip**: Read operations for LZMA and LZMA2 compression
+- **GZip**: Compression and decompression
+
+## Running Benchmarks
+
+### Run all benchmarks
+```bash
+dotnet run --project tests/SharpCompress.Performance/SharpCompress.Performance.csproj --configuration Release
+```
+
+### Run specific benchmark class
+```bash
+dotnet run --project tests/SharpCompress.Performance/SharpCompress.Performance.csproj --configuration Release -- --filter "*ZipBenchmarks*"
+```
+
+### Run with specific job configuration
+```bash
+# Quick run for testing (1 warmup, 1 iteration)
+dotnet run --project tests/SharpCompress.Performance/SharpCompress.Performance.csproj --configuration Release -- --job Dry
+
+# Short run (3 warmup, 3 iterations)
+dotnet run --project tests/SharpCompress.Performance/SharpCompress.Performance.csproj --configuration Release -- --job Short
+
+# Medium run (default)
+dotnet run --project tests/SharpCompress.Performance/SharpCompress.Performance.csproj --configuration Release -- --job Medium
+```
+
+### Export results
+```bash
+# Export to JSON
+dotnet run --project tests/SharpCompress.Performance/SharpCompress.Performance.csproj --configuration Release -- --exporters json
+
+# Export to multiple formats
+dotnet run --project tests/SharpCompress.Performance/SharpCompress.Performance.csproj --configuration Release -- --exporters json markdown html
+```
+
+### List available benchmarks
+```bash
+dotnet run --project tests/SharpCompress.Performance/SharpCompress.Performance.csproj --configuration Release -- --list flat
+```
+
+## Baseline Results
+
+The baseline results are stored in `baseline-results.md` and represent the expected performance characteristics of the library. These results are used in CI to detect significant performance regressions.
+
+To update the baseline:
+1. Run the benchmarks: `dotnet run --project tests/SharpCompress.Performance/SharpCompress.Performance.csproj --configuration Release -- --exporters markdown --artifacts baseline-output`
+2. Combine the results: `cat baseline-output/results/*-report-github.md > baseline-results.md`
+3. Review the changes and commit if appropriate
+
+## CI Integration
+
+The performance benchmarks run automatically in GitHub Actions on:
+- Push to `master` or `release` branches
+- Pull requests to `master` or `release` branches
+- Manual workflow dispatch
+
+Results are displayed in the GitHub Actions summary and uploaded as artifacts.
+
+## Benchmark Configuration
+
+The benchmarks are configured with minimal iterations for CI efficiency:
+- **Warmup Count**: 1 iteration
+- **Iteration Count**: 3 iterations
+- **Invocation Count**: 1
+- **Unroll Factor**: 1
+- **Toolchain**: InProcessEmitToolchain (for fast execution)
+
+These settings provide a good balance between speed and accuracy for CI purposes. For more accurate results, use the `Short`, `Medium`, or `Long` job configurations.
+
+## Memory Diagnostics
+
+All benchmarks include memory diagnostics using `[MemoryDiagnoser]`, which provides:
+- Total allocated memory per operation
+- Gen 0/1/2 collection counts
+
+## Understanding Results
+
+Key metrics in the benchmark results:
+- **Mean**: Average execution time
+- **Error**: Half of 99.9% confidence interval
+- **StdDev**: Standard deviation
+- **Allocated**: Total managed memory allocated per operation
+
+## Contributing
+
+When adding new benchmarks:
+1. Create a new class in the `Benchmarks/` directory
+2. Inherit from `ArchiveBenchmarkBase` for archive-related benchmarks
+3. Add `[MemoryDiagnoser]` attribute to the class
+4. Use `[Benchmark(Description = "...")]` for each benchmark method
+5. Add `[GlobalSetup]` for one-time initialization
+6. Update this README if needed