Move the auto-router path timeout check to an inner loop

The auto-router's path timeout is supposed to stop too much time being
spent on building up the set of possible routes for trains. It was being
checked once in each iteration of possible starting nodes for routes.

However, in particularly degenerate cases this meant that far too long
was elapsing between timeout checks: issue tobymao#11252 had more than
ten hours pass before the first and second timeout checks.

This moves the timeout check to an inner loop, so it is checked more
frequently.

lib/engine/auto_router.rb

@@ -64,16 +64,12 @@ def compute_for_train_group(trains, corporation, **opts)
       @next_hexside_bit = 0
 
       nodes.each do |node|
-        if Time.now - now > path_timeout
-          LOGGER.debug('Path timeout reached')
-          path_walk_timed_out = true
-          break
-        else
-          LOGGER.debug { "Path search: #{nodes.index(node)} / #{nodes.size} - paths starting from #{node.hex.name}" }
-        end
+        LOGGER.debug { "Path search: #{nodes.index(node)} / #{nodes.size} - paths starting from #{node.hex.name}" }
 
         walk_corporation = graph.no_blocking? ? nil : corporation
         node.walk(corporation: walk_corporation, skip_paths: skip_paths) do |_, vp|
+          raise PathTimeout if Time.now - now > path_timeout
+
           paths = vp.keys
           chains = []
           chain = []
@@ -163,6 +159,10 @@ def compute_for_train_group(trains, corporation, **opts)
 
           next :abort if path_abort.empty?
         end
+      rescue PathTimeout
+        LOGGER.debug('Path timeout reached')
+        path_walk_timed_out = true
+        break
       end
 
       # Check that there are no duplicate hexside bits (algorithm error)

lib/engine/game_error.rb

@@ -17,4 +17,9 @@ class RouteTooLong < GameError
 
   class ReusesCity < GameError
   end
+
+  # errors generated by the auto_router
+
+  class PathTimeout < GameError
+  end
 end