Add benchmark instrumentation and benchmark suite

bench/README.md

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+# BranchFS Benchmarks
+
+Microbenchmark suite for evaluating BranchFS performance. This suite measures **internal operation timing** by parsing daemon logs, providing accurate measurements without CLI/socket overhead.
+
+## Prerequisites
+
+```bash
+# Build branchfs
+cd ..
+cargo build --release
+
+# For plotting (optional)
+pip install matplotlib
+```
+
+## Running Benchmarks
+
+### Quick Test (Shell Script)
+
+```bash
+./quick_bench.sh
+```
+
+### Full Benchmark Suite (Python)
+
+```bash
+# Run all benchmarks
+python3 branchfs_bench.py
+
+# Quick mode (smaller parameters)
+python3 branchfs_bench.py --quick
+
+# Specific benchmark
+python3 branchfs_bench.py --bench creation   # Branch creation O(1) test
+python3 branchfs_bench.py --bench commit     # Commit latency
+python3 branchfs_bench.py --bench abort      # Abort latency
+python3 branchfs_bench.py --bench throughput # Read/write throughput
+python3 branchfs_bench.py --bench nested     # Nested branch depth
+
+# Generate LaTeX tables for paper
+python3 branchfs_bench.py --latex ../paper/
+```
+
+## Benchmarks
+
+### 1. Branch Creation Latency (O(1) Verification)
+
+Measures internal branch creation time with varying base directory sizes.
+Validates that branch creation is O(1) - constant time regardless of base size.
+
+- **Parameters**: Base sizes of 100, 1K, 10K files
+- **Expected**: ~300 µs constant latency
+
+### 2. Commit Latency
+
+Measures internal commit time for varying modification sizes.
+Validates linear scaling with modification size.
+
+- **Parameters**: Modifications of 1KB, 10KB, 100KB, 1MB
+- **Expected**: Linear increase with modification size
+
+### 3. Abort Latency
+
+Measures internal abort time. Abort only removes delta storage.
+
+- **Parameters**: Modifications of 1KB, 100KB, 1MB
+- **Expected**: Fast, independent of modification size
+
+### 4. Read/Write Throughput
+
+Measures sequential read/write throughput through FUSE layer.
+
+- **Parameters**: 50MB file, 64KB block size
+- **Output**: MB/s throughput
+
+### 5. Nested Branch Depth
+
+Measures read latency at various branch depths.
+Tests path resolution overhead.
+
+- **Parameters**: Depths 1, 2, 4, 8
+- **Expected**: Minimal increase with depth (metadata cached)
+
+## Internal Timing
+
+The benchmark parses `[BENCH]` log lines from the daemon to measure actual operation time:
+
+```
+[BENCH] create_branch 'test': 287.461µs (287 us)
+[BENCH] commit 'test': 321.194µs (321 us), 0 deletions, 1 files, 12 bytes
+[BENCH] abort 'test': 156.234µs (156 us)
+```
+
+This excludes CLI process spawn and socket communication overhead (~200ms), giving accurate internal operation times.
+
+## Output
+
+- `bench_results.json`: Raw benchmark data
+- `branch_creation_table.tex`: LaTeX table for paper
+- `commit_table.tex`: LaTeX table for paper