For Windows release builds, the `wasm_valtype_kind` C API return value
is being returned as a single byte.
The .NET interop signature for this function was expecting an
integer-sized return, resulting in three extra bytes being used on
Windows.
The fix is to limit the corresponding C# enum to a byte representation,
which will properly mask the return value from `wasm_valtype_kind`.
CI has also been updated to test both debug and release configurations
(previously it was only testing debug, hence why this was missed).
Also fixed a cast bug in the `declare_vec!` macro in the C API when the
element types were pointers to values. The `as_slice` implementation
was incorrectly casting away a level of pointer indirection, resulting
in corrupted data when accessing the slice's elements.
