docs: fix conflicting lazy heavy import guidance in STYLEGUIDE.md (#759)

[chethanuk]

📋 Summary

STYLEGUIDE.md and lazy_heavy_imports.py recommend opposite import forms for lazy-loading
heavy dependencies. from data_designer.lazy_heavy_imports import pd, np is an attribute read
against the module's PEP-562 __getattr__ facade, so it fires while the consuming module is
still importing and pandas loads eagerly — the facade buys nothing. Only
import data_designer.lazy_heavy_imports as lazy + lazy.pd stays lazy, which is what the
module's own docstring already requires and what test_lazy_imports.py already asserts. This
aligns the guide to the form that actually works.

🔗 Related Issue

Fixes #759

🔄 Changes

• STYLEGUIDE.md: rewrite the four blocks that taught the from ... import pd, np form to use
  the import ... as lazy / lazy.pd form instead. Each example gains a call site and
  from __future__ import annotations so the snippets are runnable modules rather than
  illustrations that raise NameError if copy-pasted.
• scripts/benchmarks/benchmark_engine_v2.py: convert the tree's only remaining user of the
  banned form to the alias pattern.
• packages/data-designer/tests/test_lazy_imports.py: add
  test_scripts_avoid_from_lazy_heavy_imports_pattern, extending the existing
  packages/*/src/** guard to scripts/** — the gap that let the benchmark script drift.

🧪 Testing

• make test — test_lazy_imports.py: 1 failed, 4 passed before the fix (fails on
  benchmark_engine_v2.py); 5 passed after
• make lint / make format-check — all checks passed
• make test-interface — 1119 passed, 1 skipped, 1 pre-existing failure
  (test_import_performance, an environmental make perf-import timeout under machine load,
  reproduced identically on main with none of this branch's changes applied)
• Benchmark script re-run at a fixed seed, before and after conversion: identical
  dataset_hash

✅ Checklist

• Follows commit message conventions
• Commits are signed off (DCO) — squashed to one commit, git commit -s
• Architecture docs updated — N/A (docs/test/script only, no architecture change)

Note: issue #759 does not currently carry the triaged label; the upstream
linked-issue workflow may gate on that independent of this PR.

Fixes #759

[github-actions]

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[github-actions]

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[greptile-apps]

Greptile Summary

This PR corrects the lazy-heavy-import guidance and aligns the remaining benchmark usage with the genuinely deferred import pattern.

• Rewrites STYLEGUIDE examples to use module-level lazy access with runnable, annotation-safe call sites.
• Converts the benchmark’s NumPy and pandas accesses to the lazy facade.
• Adds a regression test preventing eager facade attribute imports under scripts/**.

Confidence Score: 5/5

The PR appears safe to merge, with the documentation, benchmark conversion, and regression test consistently enforcing the intended lazy-import behavior.

The lazy facade returns and caches the real dependency modules, all converted accesses are behaviorally equivalent, and the new test correctly detects the prohibited import pattern in the intended scripts tree.

Important Files Changed

Filename	Overview
STYLEGUIDE.md	Replaces eager from-import examples with accurate lazy module-alias guidance and concrete call sites.
packages/data-designer/tests/test_lazy_imports.py	Adds a correctly rooted recursive guard against eager lazy-facade imports in Python scripts.
scripts/benchmarks/benchmark_engine_v2.py	Preserves benchmark behavior while deferring NumPy and pandas imports until their first runtime use.

_{Reviews (1): Last reviewed commit: "docs: teach the lazy import form that is..." | Re-trigger Greptile}