fix(quad): reject zero pitch instead of emitting NaN pads (#871)

[yanyishuai]

Summary

Fixes #871 — explicit zero pitch on quad-family footprints (lcc_p0mm, qfn16_p0mm, etc.) no longer silently produces NaN/null pad coordinates.

Root cause

quadTransform used truthiness checks on v.p. Explicit p=0 is falsy, so body sizing / pad sizing were skipped and getQuadCoords later computed NaN.

Fix

• Validate that p / px / py are positive finite numbers and throw a clear error otherwise
• Replace truthy v.p checks used for size inference with v.p > 0

Test plan

• tests/quad-zero-pitch.test.ts — zero pitch throws; valid lcc pads stay finite
• CI

Wallet

Do4v7foHJvRJLpRRoGaVPWX6DDEjX3yTK7J91gpwUQpE