Harden cc_heap removal, duplicates, and growth

[Dikluwe]

Summary

• repair arbitrary removal in either heap direction
• keep pointer indices coherent when duplicate pointers are stored
• rebuild every matching occurrence during cc_heap_update()
• normalize zero initial capacity to one while keeping the heap empty
• return FALSE without mutation when remove/update support is disabled
• reject a null comparator and leave the heap unchanged if growth fails
• keep the public heap header usable from C as well as C++

Security and compatibility

PR #624 fixed the zero-capacity growth bug that could write beyond a zero-byte allocation. This PR preserves that invariant without forbidding the public input: a requested capacity of zero now creates a valid empty heap with an internal capacity of one.

Growth is checked for overflow and uses a temporary allocation result. If allocation fails, existing storage and elements remain intact. Because cc_heap_add() has no return value, a failed growth attempt is a documented no-op.

The scheduler and SbTesselator callers were audited: they use positive initial capacities and enable removal support, so their behavior is unchanged.

Regression coverage

The tests cover:

• zero initial capacity
• arbitrary removal that must reheapify upward
• duplicate pointer insertion, removal, and update
• remove/update calls when removal support is disabled
• null comparator rejection
• growth from a single slot
• compilation of Inventor/C/base/heap.h as C during configuration

Local verification

• full Debug build and CTest: 9/9 passed
• full Debug build with ASan and UBSan: 9/9 passed
• public heap header verified with GCC C11, C17, and C2x
• git diff --check passed

The branch is consolidated as three focused commits directly on the current master.

[veelo]

Thanks for your work, much appreciated!