Function parse_filter_string 

pub fn parse_filter_string(raw: &str) -> Result<ParsedFilter, Error>

Parse a raw $filter string into internal AST with complexity metadata.

This function encapsulates the parsing logic and node counting.

Errors

• Error::InvalidFilter if the filter string is malformed or parsing fails

Example

let result = parse_filter_string("name eq 'John' and age gt 18")?;
if result.node_count() > MAX_NODES {
    return Err(Error::InvalidFilter("too complex".into()));
}