Do not enforce API processing timeout for parallel routing

[vpaturet]

Summary

As reported in #5110, deadlocks can occur when the parallel routing feature is activated. This is a regression caused by #5047:
To propagate the timeout to other threads, the initial ForkJoinPool/CompletableFuture logic used in parallel routing has been replaced by a fixed thread pool, because ForkJoinPool does not propagate interruptions.
But the work-stealing properties of the ForkJoinPool are necessary to prevent deadlocks.

This PR reverts to a ForkJoinPool implementation for the parallel routing use case.
This change does not impact API processing timeout when parallel routing is not in use.

Note: The parallel heuristic feature does not trigger deadlocks since it uses its own thread pool and does not create sub-tasks.

OpenTripPlanner/src/main/java/org/opentripplanner/raptor/service/RangeRaptorDynamicSearch.java

Line 169 in 9eb6235

private void runHeuristicsInParallel() {

Issue

closes #5110

Unit tests

✅

Documentation

Updated documentation

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: +0.03 🎉

Comparison is base (538ef07) 64.75% compared to head (af91e92) 64.78%.

Additional details and impacted files

@@              Coverage Diff              @@
##             dev-2.x    #5114      +/-   ##
=============================================
+ Coverage      64.75%   64.78%   +0.03%     
- Complexity     14123    14126       +3     
=============================================
  Files           1729     1728       -1     
  Lines          67369    67352      -17     
  Branches        7217     7215       -2     
=============================================
+ Hits           43623    43633      +10     
+ Misses         21324    21296      -28     
- Partials        2422     2423       +1     

Impacted Files	Coverage Δ
...entripplanner/routing/algorithm/RoutingWorker.java	78.44% <0.00%> (ø)
.../algorithm/raptoradapter/router/TransitRouter.java	75.67% <0.00%> (ø)
...r/standalone/config/routerconfig/ServerConfig.java	100.00% <ø> (ø)
...ntripplanner/standalone/server/MetricsLogging.java	0.00% <ø> (ø)

... and 1 file with indirect coverage changes

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[leonardehrenfried]

I think this is an acceptable solution to a hard problem, so I approve. We should probably discuss this a bit during the meeting.