Add memory benchmark script and reporting

[pankaj28843]

Goal

Provide a repeatable memory profiling script to detect allocation regressions over time.

Tasks

• Add benchmarks/memory.py using tracemalloc (and optional psutil) to record peak/total allocations.
• Emit JSON output for each case in benchmarks/data/.
• Document usage in benchmarks/README.md.

Dependencies

• Depends on: benchmark harness + sample corpus (already added).
• Blocks: memory regression gating policy.