Implement SPDIP footprint with spdip28 support

[Heyzerohey]

Closes #180

/claim #180

Implements the Shrink Plastic Dual In-line Package (SPDIP) footprint generator with a default 1.778mm (70mil) pin pitch and 300mil row spacing, registering support for spdip28.

[Heyzerohey]

Hi! All CI checks are completely green and passing for this implementation.

This PR implements the SPDIP (Shrink Plastic Dual In-line Package) footprint generator with a default 1.778mm (70mil) pin pitch and 300mil row spacing. It registers full support and includes robust tests for spdip28.

Could we please get this reviewed and merged? Thank you!

[Heyzerohey]

Hi @seveibar! Polite follow-up on this. All CI checks are 100% green and passing. This PR cleanly implements the SPDIP (Shrink Plastic Dual In-line Package) footprint generator with a default 1.778mm pin pitch and 300mil row spacing, registering full support and tests for spdip28. Could you please take a quick look when you have a moment? Thank you so much!

[rushabhcodes]

add kicad parity test

[Heyzerohey]

Hi @rushabhcodes! Official KiCad libraries (e.g. Package_DIP.pretty) do not contain footprints for SDIP/SPDIP (Shrink Dual In-line Package) packages (which have a 1.778mm / 70 mil pitch instead of the standard 2.54mm pitch). Since there is no standard footprint in KiCad to fetch and compare against, a KiCad parity test cannot be written for spdip28. However, we have implemented thorough unit and snapshot tests in tests/spdip.test.ts to verify the pin count, 300mil row spacing, and 1.778mm pitch dimensions directly.