use bound-fn instead of fn

the logging context is a dynamic bound variable, which is a thread local binding. when you do chain, it will kick off the function on a different thread & you’ll lose any thread local bindings. bound-fn will create the fn and preserve those

personally, for most use cases, I recommend simply using the go-off macro instead of directly using chain. It automatically keeps thread local bindings so you don’t have to worry about it yourself see https://github.com/clj-commons/manifold/blob/master/doc/deferred.md#go-off