chore: simplify debug logging for app readiness checks

[DiscreteTom]

Description of changes:
Simplify debug logging for app readiness checks to prevent abusing the logs. Move the original "app is not ready" to the trace log level.

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[mxfactorial]

easier to test

struct Checkpoint {
    start: Instant,
    interval: i32,
    next: i32,
};

impl Checkpoint {
    fn new() -> Checkpoint {
        let interval: i32 = 2;
        let start = Instant::now();
        Checkpoint {
            start,
            interval,
            next: start.elapsed().as_secs() as i32 + interval,
        }
    }

    fn increment(&mut self) {
        self.next += self.interval;
    }

    fn lapsed(&self) -> bool {
        if self.start.elapsed().as_secs() as i32 >= self.next {
            true
        } else {
            false
        }
    }
}

[bnusunny]

LGTM