refactor(track): the sleeper layout split by concern instead of one TrackSleepers.cpp

- SleeperRules: the rules beams are laid by and the faults counted where the layout breaks them
- SleeperGeometry: plan helpers, beam boxes with their overlap and support tests and a grid of cells, shared by laying, filling
  gaps, keeping beams apart and checking instead of three copies of each
- SleeperPaths: sampled paths, how near they run and whether one carries another; the tracks near a track and the stretches of
  a path where a test holds, shared by paths_around/unsettle_around and shared_zones/zones_of
- SleeperFeatures: frogs and crossings the timbers turn to; SleeperLines: lines of beams, the rails they carry, where they part
- SleeperLayout: clusters and their layout, given the epoch instead of reading it; SleeperModels: the models of the beams
- SleeperWorker: the layouts kept per epoch and worked out in the background, behind a small interface
- TrackSleepers: the facade, laying the instances, the shared zones and the check
- sleepercheck reports a digest of all beams; geomhash skips empty chunks instead of crashing

The layout is unchanged: geomhash, sleepercheck with the digest, wings, space, guards, crossings and switches give the same
output on baltyk, zz_rozjazdy_id4, zz_rf_slips, zz_rf_wide, zz_slips_s42, zz_demo_przechylka and zz_connections.

world/SleeperLayout.h

@@ -0,0 +1,38 @@
+/*
+This Source Code Form is subject to the
+terms of the Mozilla Public License, v.
+2.0. If a copy of the MPL was not
+distributed with this file, You can
+obtain one at
+http://mozilla.org/MPL/2.0/.
+*/
+
+#pragma once
+
+#include <cstdint>
+#include <map>
+#include <memory>
+#include <utility>
+#include <vector>
+
+#include "world/TrackSleepers.h"
+
+// the beams of a cluster of tracks laid out together
+namespace track_sleepers {
+
+// the beams of a cluster of tracks laid together, by the track each is laid with
+struct cluster_beams {
+    std::uint64_t epoch { 0 };
+    std::map<TTrack const *, std::vector<beam>> beams;
+};
+
+// the tracks whose timbers are laid together with those of the track: all those reached from it through paths whose plain
+// sleepers would meet, in the order of their names
+std::vector<TTrack *> cluster_of( TTrack &Track );
+// the beams of the tracks of a cluster, laid out together for the layout of the given epoch
+std::shared_ptr<cluster_beams> lay_out( std::vector<TTrack *> const &Tracks, std::uint64_t const Epoch );
+// how far the paths of the switch stand off one plane where they share the timbers of its panel, and where along the diverging
+// path; the switch itself is out of shape for its timbers where it's more than the tolerance
+std::pair<double, double> panel_off_plane( TTrack &Track );
+
+} // namespace track_sleepers