fp.h is now part of math.h

This reverts commit a17ffad.

[runtime-cxxmodules] Add overlay entry for MacOSX15.2

[runtime-cxmodules] Use separate modulemap for macOS15.2

Fix build issue on macOS 15.4 / XCode 16.3

`less` is defined in functional according to the C++ standard.

Revert "Remove the deprecated Pythia 6 interface"

This reverts commit 4e30f26.

tree: Don't leaked swapped buffer

Revert "Remove the deprecated Pythia 6 interface"

This reverts commit 4e30f26.

[geom] New BVH/VoxelGrid-based implementation of TGeoParallelWorld ro…

…utines

This commit provides a rewrite of key functions of TGeoParallelWorld, achieving:
(a) faster initialization
(b) faster execution of the Safety function (from ~O(N) to ~O(1))
(c) similar execution of FindNode/FindBoundary functions (~log(N))
(d) less memory consumption (better memory scalability)

The development for this commit was motivated from a use case in ALICE,
in which the parallel world "scene" can be very large (~100K volumes).
In this case, TGeoVoxelFinder takes very long
to construct and consumes a very large amount of memory (GBs). In addition,
the evaluation of the Safety function dominates the Geant simulation time.

The improvements in this commit are mainly achieved through:

* The use of a boundary volume hierarchy (BVH) as the base
acceleration entity, replacing TGeoVoxelFinder.
BVH are the standard in industry/computer-graphics, for what
concerns ray-object intersection tasks. The BVH is constructed
from axis-aligned bounding boxes and employed in the FindBoundary/FindNode
implementations

* The use of a 3D voxel grid (TGeoVoxelGrid) structure, able
to store properties "local" or in the vicinity of a cartesian coordinate P.
This structure allows to reduce the (typical) algorithmic complexity for "Safety" queries
to ~O(1) (with a constant factor determined by the voxel size). Filling of the 3D voxel grid cache
for Safety is done on-the-fly (using the BVH once).

Ideas for these improvements come from prior work in related libraries such as VecGeom.

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Implementation details:

* The implementation is, for now (until fully tested), provided in a backward compatible manner:

  - By default, nothing changes
  - Users have to activate the BVH mode via TGeoParallelWorld::SetAccelerationMode
  - Users may hence compare the 2 modes or choose the best depending on complexity and needs

* Functions for Safety, FindNode, FindBoundary dispatch to some internal implementation.
  This causes an extra lookup/jump, which can be removed once BVH is fully validated

* For the BVH, a well known open source implementation is included in header-only form.
  The headers are copied from https://github.com/madmann91/bvh commit 66e445b92f68801a6dd8ef943fe3038976ecb4ff.
  Some minor patching has been done in order to achieve compilation for C++17 (see README).

* A new class, TGeoVoxelGrid is provided for the cartesian VoxelGrid container.

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Performance examples:

In a test with the ALICE simulation framework including the ITS + TPC detectors
with 48240 volumes on the parallel world, we see

* initialization time goes from TGeoVoxelFinder: 10s ---> BVH: 40ms
* Geant simulation time: 10s --> 2s
* memory usage: 3GB --> 1GB

Hence, this PR will make a big difference for the ALICE simulation program.
It was verified, that identical results (number of hits, steps, etc) are obtained
when going from TGeoVoxelFinder --> BVH+GRID.

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Outlook:

Similar techniques could be applied to ordinary TGeoNavigator routines.

Fix SOFIE-ONNX compilation on macOS