Function to_value_parser

Currently used to create 'try_readers', which are readers (or reader functions, at least) that are basically composable InputType -> IResult parsers, that our normal read function / reader will wrap. Takes a parser, such as one that reads a &str and returns an i32, and creates a new parser that instead returns a valid ClojureRS Value instead

(
    parser: impl Fn(I) -> IResult<I, O>,
)