This is being emitted with [GCC 10.2.1](https://packages.debian.org/bullseye/g++-arm-linux-gnueabihf), in some CI jobs: i.e https://github.com/bitcoin/bitcoin/pull/25972/checks?check_run_id=12423693655, or https://github.com/bitcoin/bitcoin/pull/25972/checks?check_run_id=12423693651 (where we actually turn on all our warning flags with depends builds).
```bash
In file included from test/miniscript_tests.cpp:19:
./script/miniscript.h:1197:71: error: comparison of integers of different signs: 'typename iterator_traits<int *>::difference_type' (aka 'int') and 'const uint32_t' (aka 'const unsigned int') [-Werror,-Wsign-compare]
                    return std::count(subs.begin(), subs.end(), true) >= node.k;
                           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^  ~~~~~~
test/miniscript_tests.cpp:346:34: note: in instantiation of function template specialization 'miniscript::Node<CPubKey>::IsSatisfiable<(lambda at test/miniscript_tests.cpp:346:48)>' requested here
        bool satisfiable = node->IsSatisfiable([](const Node&) { return true; });
                                 ^
1 error generated.
```

cc @darosior 
InputStack(std::vector<unsigned char> in) : size(in.size() + 1), stack(Vector(std::move(in))) {}
    
    InputStack& SetAvailable(Availability avail);
    
    InputStack& SetWithSig();
    
    InputStack& SetNonCanon();
    
    InputStack& SetMalleable(bool x = true);
    
    friend InputStack operator+(InputStack a, InputStack b);
    
    friend InputStack operator|(InputStack a, InputStack b);
};
static const auto ZERO = InputStack(std::vector<unsigned char>());
static const auto ZERO32 = InputStack(std::vector<unsigned char>(32, 0)).SetMalleable();
static const auto ONE = InputStack(Vector((unsigned char)1));
static const auto EMPTY = InputStack();
static const auto INVALID = InputStack().SetAvailable(Availability::NO);
struct InputResult {
    InputStack nsat, sat;
    template<typename A, typename B>
    InputResult(A&& in_nsat, B&& in_sat) : nsat(std::forward<A>(in_nsat)), sat(std::forward<B>(in_sat)) {}