Function validate_and_prepare_time_alert 

pub fn validate_and_prepare_time_alert(
    name: &str,
    alert_time_ns: UnixNanos,
    allow_past: Option<bool>,
    ts_now: UnixNanos,
) -> Result<(Ustr, UnixNanos)>

Validates and prepares parameters for setting a time alert.

Handles name validation, default value unwrapping, and past timestamp adjustment.

Errors

Returns an error if the name is invalid or if the alert time is in the past when not allowed.