feat(bench): add AggOp memory profiler

[tristanle22]

Summary

Adds a memprofile bench binary for profiling per-AggOp structural memory usage against the workloads. This is the first part of #68, which enables further analysis.

Linked issues

Related to #68

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What changed

This PR adds a memprofile bench binary that profiles structural memory usage for each AggOp in the fraud workload. It introduces reusable MemUsage / MemProfile accounting in beava-core, generates a ranked Markdown report of per-op stack and heap estimates, and highlights the largest memory contributors.

Verification

Paste the summary block from bash .github/scripts/check.sh here so the
reviewer can see the local run passed:

PASS  cargo fmt --all --check  (0s)
PASS  cargo clippy --workspace --all-targets --features testing -- -D warnings  (1s)
PASS  cargo test --workspace --features testing  (22s)
PASS  ruff check python/  (0s)
PASS  mypy --strict beava/
PASS  pytest python (v0 acceptance suite)  (16s)

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Pre-flight checklist

• bash .github/scripts/check.sh exits 0 (or each step passes manually)
• Verification block above replaced with real output
• Docs updated (docs/*.md, beava-website/project/docs/, decorator docstrings) if user-visible behavior changed
• No stale repository URLs (canonical: beava-dev/beava)
• If this commits a schema change to beava-website/deploy/site-metrics-pipeline.json, called out in this PR body — the deploy workflow re-registers with force=true, which silently lands destructive edits