smaller simultaneous clang-format on the same file

Introducing navigation classes that estimate safety and do the "level locate"
operation using the voxel structure managed by FlatVoxelManager.

In the large daughter limit, this provides better scaling than just using
the estimators based on BVH structure, since "safety" and "locate"
are very local operations.

This is a very first version for demonstration purposes.

Future directions/work will involve:
  a) automatic tuning of the right voxel size/structure
  b) combination of voxel structure with SIMD BVH
  c) speeding up creation of voxel structure
     (it is multi-threaded but we can make use of SIMD and GPU)

Adapt benchmark for SafetyEstimator accordingly.

A singleton instance keeping, per logical volume, flat (cubic) voxel structures for
locate and safety calculations.
Follows the logic from similar existing manager classes.

Make a helper function of BoxSafetyEstimator public static so that it can be used
outside (minor clang-format cleanup included).

Add interface not needing NavigationStates but only volume types.
Useful for Geant4 integration.

Make NavigationKernelBenchmarker more realistic by using a configurable
finite physics step.

Avoid call to daughters when safety to mother is 0.

A regular (but sparse) voxel structure keeping
an arbitrary list of properties per voxel.

Useful to complement acceleration approaches
based on aligned bounding boxes for calculations
of safety and locate. Instead of searching the full
list of bounding boxes we can in future keep a reduced
list per voxel.

An API resembling what Geant4 needs.

Cleanup of some old uncommented code.

It is better not to ask every sub-class to implement it
if not needed.