feat: blocking appender for rolling file and syslog

[tisonkun]

This closes #96

[tisonkun]

@andylokandy maybe flush should return anyhow::Result<()> and we handle error all at one level up:

    fn log(&self, record: &Record) {
        for dispatch in &self.dispatches {
            if let Err(err) = dispatch.log(record) {
                handle_error(record, err);
            }
        }
    }

    fn flush(&self) {
        for dispatch in &self.dispatches {
            if let Err(err) = dispatch.flush() {
                handle_flush_error(err);
            }
        }
    }

also maybe add a ErrorSink trait for custom error listener.

[andylokandy]

I think we can keep the behavior in sync with non-blocking its variant. is the non blocking one return result on flush?

[tisonkun]

The non-blocking one do flush in the worker thread where the error is handled as eprintln!("failed to write log: {err}");.

[andylokandy]

I'm curious why BlockingRollingFile is necessary since there RollingFile. It should be intuitive that RollingFile is blocking if non_blocking is not used.

[tisonkun]

It should be intuitive that RollingFile is blocking if non_blocking is not used.

RollingFile accepts always NonBlocking. Do we have some way to paramizied this?

[andylokandy]

RollingFile accepts always NonBlocking. Do we have some way to paramizied this?

Sound reasonable. I'll take some time to play with it.