Allow `RollingFileAppender` to be set as writer

[leshow]

Feature Request

AFAIK it isn't currently possible to create a file appender without using non_blocking as with_target takes MakeWriter, which RollingFileAppender does not implement.

ex.

            let appender = tracing_appender::rolling::never("", "log");
            let fmt = fmt::layer()
                .with_writer(appender);

returns:

error[E0277]: expected a `Fn<()>` closure, found `RollingFileAppender`
  --> bin/src/logs.rs:31:40
   |
31 |     let fmt = fmt::layer().with_writer(appender);
   |                                        ^^^^^^^^ expected an `Fn<()>` closure, found `RollingFileAppender`
   |
   = help: the trait `Fn<()>` is not implemented for `RollingFileAppender`
   = note: wrap the `RollingFileAppender` in a closure with no arguments: `|| { /* code */ }`
   = note: required because of the requirements on the impl of `MakeWriter` for `RollingFileAppender`

the suggestion to wrap in a closure does not work either as the closure will be FnOnce instead of Fn

Crates

tracing_appender?

Motivation

see above

Proposal

Maybe create a blocking function that wraps RollingFileAppender in an Arc<Mutex<>> or something like that so the clones are cheaper?

I'm happy to submit a PR for this if you could give some direction on what would be the best way to solve.

[hawkw]

I believe this was added in #1760