Fix JST PH footprint to generate correct number of pads

[BoozeLee]

• Parse pin count from footprint string (e.g., jst_ph_4 → 4 pins)
• Update generatePads() to dynamically create pads for PH variant
• Add tests for jst_ph_4 and jst_ph_6 footprints

Fixes #495

Before: jst_ph_4 only generated 2 pads (hardcoded)
After: jst_ph_4 correctly generates 4 pads
/claim #495

[BoozeLee]

Hi @seveibar! 👋

This PR fixes the bug reported in #495 where JST PH
footprints with more than 2 pins were only
generating 2 pads.

The fix:

• ✅ Parses pin count from footprint strings (e.g.,
  jst_ph_4 → 4 pins)
• ✅ All 356 tests passing (added 2 new tests)
• ✅ Follows the same pattern as JST SH variant

Would it be possible to add a bounty to #495? This
was a clear bug with a well-defined solution, and
I'd love to continue contributing to tscircuit! 🚀

Thanks for maintaining such a great project!

[BoozeLee]

Following up on the inquiry regarding a bounty for issue #495. This PR (labeled 'Bounty claim') is open. Please advise on the bounty status or next steps.