Remove or document second field in `Value::Number`

Value::Number should be changed from a tuple variant to a struct variant so that the field names are self documenting.
Something like: `Number { value: String, long: bool }`

Possibly the long field could be just removed instead but not im not very familar with various SQL languages.

Start by locating the Value::Number definition and every constructor and pattern match that uses it. Check the supported SQL dialects to determine whether the long field is required; done means the variant is self-documenting or the field is removed, with all references compiling and the existing tests passing.

Written by the indexing model from the issue text.