fix: adhoc fix session leak

[ariesdevil]

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Summary

Fix session leak, to detect it, just wrap Arc<Session> to SessionWrapper as following, then check the new and drop are paired:

pub struct SessionWrapper {
    id: usize,
    session: Arc<Session>,
}

impl SessionWrapper {
    pub fn new(s: Arc<Session>) -> Self {
        let backtrace = Backtrace::force_capture();
        let backtrace = format!("{:?}", backtrace);
        let id = GlobalSequence::next();
        println!(
            "session wrapper {} new: {}-{}",
            id,
            Arc::strong_count(&s),
            backtrace
        );
        Self { id, session: s }
    }
}

impl Clone for SessionWrapper {
    fn clone(&self) -> Self {
        Self::new(self.session.clone())
    }
}

impl Drop for SessionWrapper {
    fn drop(&mut self) {
        let backtrace = Backtrace::force_capture();
        let backtrace = format!("{:?}", backtrace);
        println!(
            "session wrapper {} dropped: {}-{}",
            self.id,
            Arc::strong_count(&self.session),
            backtrace
        );
    }
}

impl Deref for SessionWrapper {
    type Target = Arc<Session>;

    fn deref(&self) -> &Self::Target {
        &(self.session)
    }
}

NOTE: this is just an ad-hoc fix, the refactoring of session module will be done related to this issue

Fixes #6560

[vercel]

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Name	Status	Preview	Updated
databend	✅ Ready (Inspect)	Visit Preview	Jul 18, 2022 at 3:14PM (UTC)

[drmingdrmer]

I'm not sure about the root cause of this leak, although I partially get involved in the tracing for this problem.

After all, these modification looks good to me:
Always using SessionRef and making the call stack shallow will makes the codebase more clear and easier to understand.