mermaid-render: python: render_to_png PyO3 wrapper (gated)

[hartsock]

Phase: 5 • Branch: mermaid-render/5.2-py-render-to-png

What

Same as 5.1 for render_to_png. Surfaced only when the png feature is enabled at build time; absent otherwise.

Files

• scrybe-mermaid-render/src/python.rs

Tests

• 3+ Rust unit tests (feature-gated): returns bytes, valid PNG header, error propagation.

Acceptance

• maturin develop --features png exposes render_to_png; default build does not.

Refs

#37 • swarm.toml phase-5 goal 0.

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