feat: strip indentation from source code

[Sl1mb0]

Closes #141

This creates a UdfCodeFormatter trait that allows us to format UDF code how we see fit before compiling it. A StripIndentationFormatter implementation is also provided that strips indentation from source code.

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[crepererum]

I think this needs a clean rebase

[crepererum]

The fact that the empty line is indented or not is impossible to see in this diff. I suggest that for the indentation tests you don't use multi-line strings but rather an array like this:

let query = &[
    "CREATE FUNCTION add_one()",
    // or
    "    CREATE FUNCTION add_one()",
    ...
    // this is an non-indended empty line:
    "",
    // and this one would be indended:
    "    ",
];

[crepererum]

For both it probably also makes sense to derive Default