Add SPDIP-28 footprint alias

[Golradreth]

Summary

• normalize SPDIP package strings such as spdip28 and SPDIP-28_W7.62mm to the existing DIP generator
• add focused parser/render snapshot coverage for spdip28
• add KiCad parity coverage against Package_DIP.pretty/DIP-28_W7.62mm
• include generated snapshots so the rendered footprint is visible in review

Tests

• bun test tests\spdip.test.ts tests\kicad-parity\spdip28_kicad_parity.test.ts
• bun run build
• bun test

Fixes #180