Function process_file 

pub fn process_file(
    input: &str,
    output: &str,
    filter_keys: &[String],
    processor: &'_ mut dyn FnMut(TypedValue, ValueType, &str) -> Result<(TypedValue, ValueType, ProcessHandling), Box<dyn Error>>,
) -> Result<(), Box<dyn Error>>

Read a JSON file, apply processor to every matching scalar value, and write the result. filter_keys is a list of dot-notation key paths to restrict processing to; empty means all values. Key insertion order is preserved via serde_json’s preserve_order feature.