Fix and actually test the sat stack elements calculation

There are unit tests to exerce the calculation of the maximum number of elements of a satisfaction:
https://github.com/rust-bitcoin/rust-miniscript/blob/a2d6fff55a6b4a81a92fe740ee4dea86746875cc/src/miniscript/mod.rs#L586-L631

However they are not executed...
https://github.com/rust-bitcoin/rust-miniscript/blob/a2d6fff55a6b4a81a92fe740ee4dea86746875cc/src/miniscript/mod.rs#L570

Actually executing them makes the test fail. It looks like most vectors were taken from the C++ implem and therefore the Rust implem of the calculation is not on par with the C++ one.

diff --git a/src/miniscript/mod.rs b/src/miniscript/mod.rs
index c20ed89..2b4d0da 100644
--- a/src/miniscript/mod.rs
+++ b/src/miniscript/mod.rs
@@ -567,7 +567,7 @@ mod tests {
         non_mal: bool,
         need_sig: bool,
         ops: usize,
-        _stack: usize,
+        stack: usize,
     ) {
         let ms: Result<Segwitv0Script, _> = Miniscript::from_str_insane(ms);
         match (ms, valid) {
@@ -576,6 +576,7 @@ mod tests {
                 assert_eq!(ms.ty.mall.non_malleable, non_mal);
                 assert_eq!(ms.ty.mall.safe, need_sig);
                 assert_eq!(ms.ext.ops_count_sat.unwrap(), ops);
+                assert_eq!(ms.ext.stack_elem_count_sat.unwrap(), stack);
             }
             (Err(_), false) => return,
             _ => unreachable!(),

A quick look at the first vector failing with the above patch suggests that this is the calculation that needs to be fixed: the vector looks right.
https://github.com/rust-bitcoin/rust-miniscript/blob/a2d6fff55a6b4a81a92fe740ee4dea86746875cc/src/miniscript/mod.rs#L610

Start in src/miniscript/mod.rs around the satisfaction stack-element tests at lines 570-631. Enable the stack count assertion shown in the issue, run the unit tests, and inspect the first failing vector and its calculation. Done means the tests execute and the Rust calculation matches the expected vectors.