Decide on a name for `MultiUseSandbox::set_log_level` / `MultiUseSandbox::log_level`

[jprendes]

I believe in general we don't use the set/get prefixes much in Rust. I'll leave it as it is now, but we can have a follow up discussion and change it with a follow up PR.

@yoshuawuyts , I'm almost sure you have some opinion on this.

Originally posted by @jprendes in #1833 (comment)