Move the actor logs into the trace

[Stebalien]

At the moment, when actor debugging is enabled logs are written to stdout. Instead, we should record them in the execution trace inside of the call manager. I.e., each log becomes an ExecutionEvent:

ref-fvm/fvm/src/trace/mod.rs

Lines 21 to 40 in ed6d34a

	pub enum ExecutionEvent {
	GasCharge(GasCharge),
	/// Emitted on each send call regardless whether we actually end up invoking the
	/// actor or not (e.g. if we don't have enough gas or if the actor does not exist)
	Call {
	from: ActorID,
	to: Address,
	method: MethodNum,
	params: Option<IpldBlock>,
	value: TokenAmount,
	gas_limit: u64,
	read_only: bool,
	},
	CallReturn(ExitCode, Option<IpldBlock>),
	CallError(SyscallError),
	/// Emitted every time an actor is successfully invoked.
	InvokeActor {
	id: ActorID,
	state: ActorState,
	},

If we do this, it should become much easier to debug actors from clients. Instead of having to:

1. Restart the client with some env var enabled.
2. Read stdout/stderr.

We can invoke the FVM with debug tracing enabled and return the serialized logs over RPC.

[Stebalien]

We'll need to eventually call:

ref-fvm/fvm/src/call_manager/default.rs

Lines 522 to 531 in ed6d34a

	fn trace(&mut self, trace: ExecutionEvent) {
	// The price of deref magic is that you sometimes need to tell the compiler: no, this is
	// fine.
	let s = &mut **self;
	s.exec_trace
	.extend(s.gas_tracker.drain_trace().map(ExecutionEvent::GasCharge));
	s.exec_trace.push(trace);
	}

From:

ref-fvm/fvm/src/kernel/default.rs

Lines 954 to 956 in ed6d34a

	fn log(&self, msg: String) {
	println!("{}", msg)
	}

But we don't currently export DefaultCallManager::trace. Personally, I'd add a log method to the CallManager that just takes a string and internally calls trace() to record it in the trace.