Add SPDIP-28 footprint alias

[DrOetker747]

/claim #180

Adds SPDIP string normalization for the existing DIP footprint generator so common package names such as SPDIP-28, spdip28, and parameterized forms like spdip28_w7.62mm resolve through the same implementation as dip28.

This keeps skinny/plastic DIP naming variants on the same DIP geometry path instead of adding a duplicated footprint generator.

Verification run locally:

• npm exec -- biome check src/footprinter.ts tests/dip.test.ts
• npm run build
• direct Node check against the built package confirming SPDIP-28 and spdip28 produce the same JSON as dip28
• git diff --check

Notes:

• The repo expects bun test, but bun is not installed in this environment, so I could not run the Bun test suite directly.