Validate MtlArray storage mode

Check if 3rd argument of MtlArray (`S`) is a valid `MTL.MTLStorageMode` and throw ArgumentError for unsupported values.

Author: pvprajwal

src/array.jl

@@ -52,6 +52,13 @@ mutable struct MtlArray{T,N,S} <: AbstractGPUArray{T,N}
 
     function MtlArray{T,N,S}(::UndefInitializer, dims::Dims{N}) where {T,N,S}
         check_eltype(T)
+
+        try
+            convert(MTL.MTLStorageMode, S)
+        catch
+            throw(ArgumentError("Invalid MTL storage mode: $S. Must be one of Metal.PrivateStorage, Metal.SharedStorage or Metal.ManagedStorage."))
+        end
+        
         maxsize = prod(dims) * sizeof(T)
 
         bufsize = if Base.isbitsunion(T)