feat: better generic args

[sjrusso8]

Description

feat(generics): better generic args

• add better generic types to traits
• add new trait implementation for an array of expressions
• update example

Example

Allow for statements like this in the select method.

df.select(["id", "value"])

// or like this

df.select([col("id"), col("value")])

// or like this too

df.select(vec![col("id"), col("value")])

All of which are translated to a vector expression.

Also there is better consistently for all function inputs. The default is &str for everything where a string input is needed. So all arguments that were Vec<String> are now Vec<&str>, etc.