Some maintenance question

[Thorium]

This is not so much of an issue, but just a maintenance question...

The Utils module has lot of stuff that I think is pre-ValueOption and UOption could be replaced with VOption.
https://github.com/fsprojects/FSharp.TypeProviders.SDK/blob/master/src/ProvidedTypes.fs#L36

I think the utils themselves could also benefit of Spans, for example:
https://github.com/fsprojects/FSharp.TypeProviders.SDK/blob/master/src/ProvidedTypes.fs#L55
...could work something like:

    let splitNameAt (nm:ReadOnlySpan<char>) idx =
        if idx < 0 then failwith "splitNameAt: idx < 0";
        let last = nm.Length - 1
        if idx > last then failwith "splitNameAt: idx > last";
        (nm.Slice(0, idx)), 
        (if idx < last then nm.Slice (idx+1, last - idx) else ReadOnlySpan.Empty)

    let splitILTypeName (nm:ReadOnlySpan<char>) =
        match nm.LastIndexOf '.' with
        | -1 -> UNone, nm
        | idx -> let a, b = splitNameAt nm idx in USome a, b

I would also like to make the DUs without any fields (or only fields of plain non-recursive other DUs) as structs, e.g. here:
https://github.com/fsprojects/FSharp.TypeProviders.SDK/blob/master/src/ProvidedTypes.fs#L2737
https://github.com/fsprojects/FSharp.TypeProviders.SDK/blob/master/src/ProvidedTypes.fs#L2952
https://github.com/fsprojects/FSharp.TypeProviders.SDK/blob/master/src/ProvidedTypes.fs#L2973

Why do I even care, is because with a bigger F# solution with multiple type-providers they end-up taking quite a bit of resources, making VS a bit slow, for example this is a part of memory snapshot of VS2022:

[Thorium]

I tried to change those DUs to structs (master...Thorium:FSharp.TypeProviders.StarterPack:more-structs),
and run some memory & performance analysis with some type-providers and VS, but the difference was within mean square error margin. So no justification for the change.