Function save_results_filter_show_canonical 

pub fn save_results_filter_show_canonical(canonical_id: &str, value: bool)

What: Persist results_filter_show_<canonical> for a dynamic repo filter id from repos.conf.

Inputs:

• canonical_id: Normalized filter token (a-z, 0-9, _ only).
• value: Whether matching packages should appear in Results.

Output:

• None.

Details:

• No-op when canonical_id is empty or contains characters outside the safe token alphabet.
• Writes the full key name results_filter_show_<canonical_id> into settings.conf.