Fix intermittent double-free crash in IBM_Cylinder (PointLinkedList)

[Copilot]

The IBM_Cylinder CI test failed non-deterministically with free(): double free detected in tcache 2 → SIGABRT inside PointLinkedList_Destruct, called from ConvexHull → OBB_construct → IBM_construct.

Root cause

PointLinkedList in TessellationTypes.f90 maintained a NumOfPoints counter that was never initialized and never updated by any list operation. The destructor used this garbage value to drive its deallocation loop:

• If garbage value < actual count → memory leak (silent, test passes)
• If garbage value > actual count → loop follows circular pointers back into already-freed nodes → double-free crash

Which outcome occurred depended on what happened to be in that memory location, explaining the intermittent failure.

A secondary bug: the original destructor loop (do i = 2, NumOfPoints) freed only N−1 nodes, always leaking the last one, and on its final iteration read current%next from already-freed memory.

Changes (TessellationTypes.f90)

• PointLinkedList_Construct — initialize NumOfPoints = 0
• PointLinkedList_Add — increment NumOfPoints after insertion
• PointLinkedList_RemoveLast — decrement NumOfPoints after removal
• PointLinkedList_Remove — decrement NumOfPoints after removal
• PointLinkedList_Destruct — restructure loop to free all N nodes without reading from freed memory; nullify head on both exit paths

! Before: loop i=2..N frees only N-1 nodes, reads freed head%next on last iteration
do i = 2, this% NumOfPoints
   deallocate(current)
   current => next
   next    => current% next   ! UB on last iter: next points to freed head
end do

! After: clean separation of "advance next" from "free current"
do i = 1, this% NumOfPoints - 1
   next => current% next
   deallocate(current)
   current => next
end do
deallocate(current)  ! free last node
nullify(this% head)

[Copilot]

Pull request overview

This PR addresses a non-deterministic double-free crash in the IBM_Cylinder CI path by fixing PointLinkedList bookkeeping and making PointLinkedList_Destruct free nodes safely based on an accurate node count.

Changes:

• Initialize PointLinkedList%NumOfPoints to 0 in the list constructor.
• Maintain NumOfPoints correctly on add/remove operations.
• Rework PointLinkedList_Destruct to deallocate all nodes without dereferencing freed memory, and nullify head on exit.

---

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

[codecov]

Codecov Report

❌ Patch coverage is 54.54545% with 5 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
Solver/src/libs/mesh/TessellationTypes.f90	54.54%	3 Missing and 2 partials ⚠️

📢 Thoughts on this report? Let us know!