Function validate_filter 

pub fn validate_filter(f: &Filter) -> MenteResult<()>

Check one filter on the owner and score fields:

• agent and space compare an id (a UUID, quoted or bare) with =, !=, or IN [...].
• salience and confidence compare a number with =, !=, <, <=, >, >=, or IN [...].

Other fields keep their existing handling.