cuda.core: VirtualMemoryResourceOptions accepts values the driver rejects, and modify_allocation mishandles edge inputs #2910

Validation gaps found while analyzing #2882, each a small change: (1) addr_align larger than the granularity makes the adjacent-reservation probe fail with a misaligned hint, which is treated as fatal instead of falling back to the slow path; (2) new_size < buf.size is silently treated as an access-only update; (3) allocation_type=MANAGED is exposed but current drivers reject it in cuMemCreate; (4) modify_allocation guards a user-reachable condition with assert; (5) allocate(0) reaches the driver and fails while sibling resources return an empty Buffer; (6) the default handle_type=POSIX_FD fails on native Windows WDDM devices and on location_type="host"; (7) for host locations device_id is validated and ignored, HOST_NUMA_CURRENT can never allocate, and a host resource with peers reports is_device_accessible=False. Related: #2694.