Introduce a unified Reallocate method to all memory allocator types (Arena, Stack, FreeList, VirtualArena, VirtualStack, DynamicArena) and require it in the IMemoryAllocator interface. This enables efficient resizing of memory blocks, with fast-path optimizations for stack-like allocators.
Update AllocationManager and MemoryPool to use the new Reallocate method, simplifying and optimizing memory resizing logic. Add public properties for buffer pointers, sizes, and offsets to allocator structs for easier diagnostics.
Set FreeList's default concurrency level to 1 and make its allocation method return null on dispose instead of throwing. Clean up vector types for formatting, fix UnsafeList's RemoveRangeSwapBack logic, and simplify RemoveAtSwapBack.
Simplify Program.cs to only run SPMDBenchmark. Add new unit tests for FixedString, UnsafeList, UnsafeHashMap, and UnsafeHashSet. Apply minor test code cleanups for consistency in TestUnsafeQueue.
BREAKING CHANGE: IMemoryAllocator now requires a Reallocate method, and allocator APIs have changed accordingly.
Refactored Arena, DynamicArena, FreeList, and Stack to implement the new IMemoryAllocator<TSelf, TOpts> interface, standardizing allocation and free methods. Introduced MemoryPool<T, TOpts> for allocator lifetime management and AllocationHandle access. Updated Program.cs to use MemoryPool, replacing AllocationManager. Minor project file updates included.
Added new AllocationHandle property in Stack.Scope.
Changed the ref AllocationHandle constructor parameter to AllocationHandle on of all UnsafeCollection types
Removed Allocator.Stack. Use Stack.Scope.AllocationHandle to allocate on stack instead.
