Implement SPDIP-28

[Abse2001]

Here's are components on JLCPCB with this footprint: https://jlcsearch.tscircuit.com/components/list?package=SPDIP-28

There may be reference dimensions/designs on the kicad viewer

This issue may be eligible for a $10 bounty from the TSCircuit team (please review!)

[bitdeckai]

I can take this. Plan: add SPDIP-28 footprint parameters aligned to KiCad/JLC reference, wire it into the footprinter string mapping, and add a snapshot test to validate output.

[bitdeckai]

Opened PR: #508