Attempts to add // math operator (#5759)

* attempts to add `div` math operator

* allows `//` to be used too

* fmt:

* clippy issue

* returns appropriate type

* returns appropriate type 2

* fmt

* ensure consistency; rename to `fdiv`

* Update parser.rs

crates/nu-protocol/src/ast/operator.rs

@@ -20,6 +20,7 @@ pub enum Operator {
     In,
     NotIn,
     Modulo,
+    FloorDivision,
     And,
     Or,
     Pow,
@@ -43,6 +44,7 @@ impl Display for Operator {
             Operator::In => write!(f, "in"),
             Operator::NotIn => write!(f, "not-in"),
             Operator::Modulo => write!(f, "mod"),
+            Operator::FloorDivision => write!(f, "fdiv"),
             Operator::And => write!(f, "&&"),
             Operator::Or => write!(f, "||"),
             Operator::Pow => write!(f, "**"),