Refactored time

Treating time and conditions as the same entity was getting confusing, and it
added a lot of unnecessary abstraction in a critical part (the scheduler).

The scheduling queue now has the time as a floating number (faster), the agent
id (for ties) and the condition, as well as the agent. The first three
elements (time, id, condition) can be considered as the "key" for the event.

To allow for agent execution to be "randomized" within every step, a new
parameter has been added to the scheduler, which makes it add a random number to
the key in order to change the ordering.

`EventedAgent.received` now checks the messages before returning control to the
user by default.

examples/events_and_messages/cars.py

@@ -127,7 +127,8 @@ class Driver(Evented, FSM):
                 )
 
             self.check_passengers()
-            self.check_messages()  # This will call on_receive behind the scenes, and the agent's status will be updated
+            # This will call on_receive behind the scenes, and the agent's status will be updated
+            self.check_messages()  
             yield Delta(30)  # Wait at least 30 seconds before checking again
 
         try:
@@ -204,6 +205,8 @@ class Passenger(Evented, FSM):
         while not self.journey:
             self.info(f"Passenger at: { self.pos }. Checking for responses.")
             try:
+                # This will call check_messages behind the scenes, and the agent's status will be updated
+                # If you want to avoid that, you can call it with: check=False
                 yield self.received(expiration=expiration)
             except events.TimedOut:
                 self.info(f"Passenger at: { self.pos }. Asking for journey.")
@@ -211,7 +214,6 @@ class Passenger(Evented, FSM):
                     journey, ttl=timeout, sender=self, agent_class=Driver
                 )
                 expiration = self.now + timeout
-            self.check_messages()
         return self.driving_home
 
     @state
@@ -220,7 +222,11 @@ class Passenger(Evented, FSM):
             self.pos[0] != self.journey.destination[0]
             or self.pos[1] != self.journey.destination[1]
         ):
-            yield self.received(timeout=60)
+            try:
+                yield self.received(timeout=60)
+            except events.TimedOut:
+                pass
+
         self.info("Got home safe!")
         self.die()