fix(draw): harden geometry at extreme coordinates

[devmobasa]

Summary

• use checked or widened arithmetic for rectangle and ellipse geometry
• reject unrepresentable rectangle and blur drag spans
• centralize clipped shape-bound construction across drawing types
• reject invalid floating-point bounds and negative radii
• harden polygon templates, arrow labels, and step-marker geometry at coordinate limits

Validation

• focused utility geometry, drag normalization, and shape-bound tests
• the same focused tests with --no-default-features
• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets --all-features -- -D warnings
• git diff --check