fix(to220): use standard 2.54mm lead pitch and respect p parameter

[rudra496]

Summary

Fixes #790.

Previously, `to220` computed its pin pitch dynamically from plastic body width (`Math.max(minPitch, maxHoleWidth / (numPins - 1))`), resulting in 2.6mm pitch on the standard 3-pin part instead of the JEDEC/KiCad 2.54mm (0.1") standard pitch, while ignoring the `p` parameter.

Changes

1. Standard Pitch: Defaulted `p` to `"2.54mm"` in `to220_def`, matching JEDEC TO-220 and KiCad `TO-220-3_Vertical` standards.
2. Respect `p` Parameter: Positioned plated holes according to `pitch = parameters.p` so custom pitch overrides (e.g. `to220_3_p3mm`) function properly.
3. Unit Tests: Added `tests/to220-pitch.test.ts` verifying that `to220_3` defaults to 2.54mm pitch and respects custom `p` values.

Verification

• `bun test tests/to220-pitch.test.ts` (2/2 passing).

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