Change SelectValueType to accept readonly arrays

# Feature request

## Summary

```ts
- type SelectValueType = Multiple extends true ? Value[] : Value;
+ type SelectValueType = Multiple extends true ? readonly Value[] : Value;
```

Allow passing `readonly` (immutable) array as value for Select.

## Examples in other libraries

Maybe not the best example because it's options and not value:
https://github.com/mui/material-ui/blob/77245fd41663c22eeedd3f7072deafd7aa1284da/packages/mui-material/src/useAutocomplete/useAutocomplete.d.ts#L298

## Motivation

I'm in react, so approximately all of my arrays are readonly, and I'm trying to write correct types.

Find the SelectValueType definition in the TypeScript Select component and read its surrounding value type declarations. Update the multiple-value typing to accept readonly arrays, then run the relevant Select type checks or tests; done means readonly array values are accepted without weakening the single-value case.

Written by the indexing model from the issue text.