Fix duplicate margin in cached polyhedral AABBs

[tianrking]

Fixes #4694

Problem

btPolyhedralConvexAabbCachingShape::recalcLocalAabb() stores support bounds with the collision margin already applied. Both the virtual and nonvirtual AABB paths then pass the current margin to btTransformAabb, expanding the bounds a second time. Caching the margin also lets a later setMargin() combine a stale cached value with the new one.

Change

• Cache only the no-margin polyhedral support bounds.
• Continue applying the current margin when transforming the cached bounds.
• Add a btConvexHullShape regression covering the virtual path, the nonvirtual path, a runtime margin update, and a rotated/translated transform.

The regression fails on master with each identity-bound axis over-expanded by exactly one additional margin (for example, expected -1.25 but got -1.5).

Validation

• Release single precision: built BulletCollision and Test_Collision; all 6 collision tests pass.
• Release double precision (USE_DOUBLE_PRECISION=ON): built BulletCollision and Test_Collision; all 6 collision tests pass.
• C++98 (-std=c++98): built and ran Test_Collision; all 6 collision tests pass.
• git diff --check