Effects on branches of a match

```fstar
val q : unit -> Dv unit
let q () = ()

let test () =
(match () with
| () -> q) ()
```
This fails and requires an annotation, but looks like it should just work. It's harder to provide a good annotation when `q` has two arguments.
```fstar
open FStar.All

assume val ff : int -> int -> ML int
assume val gg : int -> int -> ML int

let rw_test4 (b:bool) : ML int =
(match b with
| true -> ff
| false -> gg
) 100 200
```
```
FStar.All.ML int is not a subtype of the expected type Prims.Tot (*?u64*) _
```

Reproduce the two F* examples from the issue, beginning with the match expressions in test and rw_test4 and their reported type errors. Trace the compiler's effect inference for match branches and verify that both examples typecheck without the extra annotation while retaining the expected Dv unit and ML int types.

Written by the indexing model from the issue text.