Clean up closest point autogen

[zfergus]

Description

Clean up the closest point auto-generated code.

[Copilot]

Pull request overview

This PR removes redundant auto-generated closest-point derivative code from smooth_contact/distance and consolidates closest-point Hessian access through the ipc::tangent closest-point utilities, reducing duplicated generated sources.

Changes:

• Replace direct calls to smooth_contact/distance autogen Hessians with edge_edge_closest_point_hessian() / point_triangle_closest_point_hessian() from ipc/tangent/closest_point.
• Delete src/ipc/smooth_contact/distance/autogen.{hpp,cpp} and remove them from the distance CMake source list.
• Update TinyAD include in autodiff_types.hpp to use TinyAD/Scalar.hh.

Reviewed changes

Copilot reviewed 6 out of 8 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/ipc/utils/autodiff_types.hpp	Switch TinyAD header include to Scalar.hh.
src/ipc/tangent/closest_point.hpp	Add public Hessian APIs + expose corresponding autogen function declarations.
src/ipc/smooth_contact/distance/point_face.cpp	Replace direct autogen Hessian calls with tangent closest-point Hessian API.
src/ipc/smooth_contact/distance/edge_edge.cpp	Replace direct autogen Hessian calls with tangent closest-point Hessian API.
src/ipc/smooth_contact/distance/autogen.hpp	Removed (duplicate generated declarations).
src/ipc/smooth_contact/distance/autogen.cpp	Removed (duplicate generated implementation).
src/ipc/smooth_contact/distance/CMakeLists.txt	Stop compiling removed autogen sources.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

You can also share your feedback on Copilot code review. Take the survey.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.19%. Comparing base (eba9e31) to head (9458ef8).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #220      +/-   ##
==========================================
+ Coverage   97.18%   97.19%   +0.01%     
==========================================
  Files         161      160       -1     
  Lines       24705    24798      +93     
  Branches      888      888              
==========================================
+ Hits        24009    24102      +93     
  Misses        696      696              

Flag	Coverage Δ
unittests	97.19% <100.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.