adapt_storage-related improvements

[christiangnrd]

This PR does 3 things:

• Adds a check for the unsupported Int128 and UInt128 when constructing a MtlArray. (Int128 does not compile #287 (comment))
• Simplifies the opinionated adapt_storage to only convert Float64 -> Float32. This also makes BigFloat no longer get converted to Float32. Add tests for every supported scalar type. (also Int128 does not compile #287 (comment))
• I forgot to add a function for the regular constructor when I parameterized the storagemode in Parameterize MtlArray storage mode #194, so add that and add tests

Closes #287
Closes #289

I can spin off point 3 into its own PR if the other 2 need more discussion.

[maleadt]

Thanks!