Report errors on, or circumvent, multiple `RefCell` borrows in Deno ops

[andreaphylum]

Currently, Deno ops (i.e. our Rust-side API) require a Rc<RefCell<OpState>> parameter for handling state. All of our ops are asynchronous, and a user not awaiting on them immediately will cause the RefCell to be mutably borrowed multiple times, which will result in a panic:

Deno.core.print(JSON.stringify(await PhylumApi.get_user_info())) // this will not panic
Deno.core.print(JSON.stringify(PhylumApi.get_user_info())) // this will panic

We need to either leverage some concurrency primitive (e.g. Mutex/RwLock), and make sure it won't ever result in a deadlock, or provide the user with actionable feedback (e.g. "please immediately await Phylum API calls"). Allowing concurrency and favoring more async-friendly interior mutability structures in place of Rc<RefCell<T>> should in general be preferred, but Deno's documentation is currently not super clear on the mechanisms that could cleanly complement that.

[cd-work]

The simplest solution would probably just to use try_borrow(_mut) to avoid panics. But we could probably store something inside the Rc<RefCell<T>> like a Mutex and still hold mutable borrows to the data itself with an async mutex.