collision: fix Bullet double-precision includes (6.16)

[jslee02]

Fixes #2332.

Background

When Bullet is built with double precision (BT_USE_DOUBLE_PRECISION=1), DART 6.16 can violate the ODR because dart/collision/bullet/BulletTypes.hpp included Bullet headers directly, bypassing dart/collision/bullet/BulletInclude.hpp (which includes dart/config.hpp first). This shows up as -Wodr warnings and runtime failures (raycast returns no hits and then segfaults; Bullet-based collision regression tests fail).

Changes

• dart/collision/bullet/BulletTypes.hpp: include Bullet via dart/collision/bullet/BulletInclude.hpp to ensure consistent Bullet precision macros across all translation units.
• tests/integration/test_Raycast.cpp: use ASSERT_* before indexing mRayHits (avoids segfault when a hit is unexpectedly missing).

Local verification

• Built against Bullet 3.25 with double precision enabled and ran: ctest -R '^(test_Raycast|test_Collision|test_ForceDependentSlip|test_Issue1184)$'.
• Ran: CMAKE_BUILD_PARALLEL_LEVEL=16 CTEST_PARALLEL_LEVEL=16 pixi run test, CMAKE_BUILD_PARALLEL_LEVEL=16 pixi run test-all, and CMAKE_BUILD_PARALLEL_LEVEL=16 pixi run -e gazebo test-gz.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.68%. Comparing base (07aef36) to head (a3962f5).

Additional details and impacted files

@@              Coverage Diff              @@
##           release-6.16    #2334   +/-   ##
=============================================
  Coverage         58.68%   58.68%           
=============================================
  Files               384      384           
  Lines             32056    32056           
  Branches           3870     3870           
=============================================
  Hits              18812    18812           
  Misses            13244    13244           

Flag	Coverage Δ
unittests	58.68% <ø> (ø)

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