[Feature] Introduce Pointer object to replace int64_t handles

[VxidDev]

Currently, Arc’s standard library handles pointers (in UI, mixer, and net modules) by casting void* to uintptr_t and storing them as int64_t. This approach is unsafe, prone to memory leaks, and makes it difficult to track pointer validity or ownership.

Proposed Solution:
Implement a dedicated Pointer object to wrap these memory addresses.

typedef struct Pointer {
    Object base;
    void* ptr;
    void (*cleanup)(void* ptr)
} Pointer;

Goals:

• Replace int64_t handles in std libraries with the Pointer object.
• Restrict arithmetic: Prevent the Arc VM/interpreter from allowing pointer arithmetic (e.g., ptr = ptr + 99 must be a compile-time or runtime error).
• Add reference counting (available through Object base) to avoid memory leaks.

Expected Outcome/Checklist:

• Create Pointer object definition.
• Add reference counting to Pointer object.
• Update UI library to use Pointer.
• Update Mixer library to use Pointer.
• Update Net library to use Pointer.
• Implement checks in the VM/compiler to block invalid pointer operations.