Improvements to internal ownership semantics

[lionel-]

• Get rid of Console::get_mut(). Use interior mutability on specific fields. Maybe with ArkRefCell that's only panicking in debug builds.

• Some of the channels consumed by the readconsole event loop shouldn't be clonable. ReadConsole is reentrant, and cloning a receiver means only one of the clones gets a message. We currently clone them, but luckily the reentrant path shuts down the event loop beforehand. We should make an unclonable wrapper to enforce the property.

  ark/crates/ark/src/console/console_repl.rs

  Lines 963 to 969 in 74efb52

  	// Cloning is necessary to avoid a double mutable borrow error
  	let r_request_rx = self.r_request_rx.clone();
  	let stdin_reply_rx = self.stdin_reply_rx.clone();
  	let kernel_request_rx = self.kernel_request_rx.clone();
  	let tasks_interrupt_rx = self.tasks_interrupt_rx.clone();
  	let tasks_idle_rx = self.tasks_idle_rx.clone();
  	let tasks_idle_any_rx = self.tasks_idle_any_rx.clone();

Not urgent (Ark is not exploding left and right) but would be nice to converge towards a safer setup.