QoL: improve query fns that take a sequence of generic arguments

1. The API currently is not easy to use as it accepts a reference to an array containing impl Operable. This causes errors when the types implementing Operable are constructed in the fn call site (temporary data dropped). To fix this issue, a generic type that implements IntoIterator<Item = T> where T: Operable can be used instead.

2. Since a generic type can only be replaced with a single concrete type, different types cannot be mixed. This disallows the use of complex queries passed as params. To fix this, an RawExpression type can be provided which holds a string on the inside and implements Operable. (for convenience, all types that implement Operable can have a blanket impl of From<T: Operable> for RawExpression.