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-command/src/database/values/dsl/expression.rs

@@ -112,6 +112,7 @@ impl CustomValue for ExprDb {
             Operator::Multiply => Ok(BinaryOperator::Multiply),
             Operator::Divide => Ok(BinaryOperator::Divide),
             Operator::Modulo => Ok(BinaryOperator::Modulo),
+            Operator::FloorDivision => Ok(BinaryOperator::Divide),
             Operator::And => Ok(BinaryOperator::And),
             Operator::Or => Ok(BinaryOperator::Or),
             Operator::In