Function maybe_to_int 

pub fn maybe_to_int(
    interp: &mut Artichoke,
    value: Value,
) -> Result<MaybeToInt, Error>

Attempt a fallible conversion of the given value to i64.

Conversion steps:

• If the given value is an Integer, return its underlying i64.
• If the value does not have a to_int method, the conversion is not applicable so return None.
• If value.to_int raises, return the exception in Err(_).
• If the value returned by the conversion is an Integer, return its underlying i64.
• Else, the conversion is not applicable so return None.