When copying host instances with bulk transfers, fewer kernels are
invoked, which reduces the overhead, and construction on the GPU runs in
parallel.
With the trackML geometry, bulk copying placed volumes and transformations
is 10x faster on a TeslaV100 GPU.
The total transfer time reduces 5x.

Diff of AdePT't example11 synchronising trackML.gdml:
```
New:                                                            Old:
INFO: using default trackML.gdml for option -gdml_name		INFO: using default trackML.gdml for option -gdml_name
INFO: using default 0 for option -cache_depth			INFO: using default 0 for option -cache_depth
INFO: using default 1 for option -particles			INFO: using default 1 for option -particles
INFO: using default 100 for option -energy			INFO: using default 100 for option -energy
(II) vgdml::Frontend::Load: VecGeom millimeter is 1		(II) vgdml::Frontend::Load: VecGeom millimeter is 1
Starting synchronization to GPU.				Starting synchronization to GPU.
Allocating geometry on GPU...Allocating logical volumes... OK	Allocating geometry on GPU...Allocating logical volumes... OK
Allocating unplaced volumes... OK: #elems in alloc_mem=2, mem	Allocating unplaced volumes... OK: #elems in alloc_mem=2, mem
Allocating placed volumes... OK					Allocating placed volumes... OK
Allocating navigation index table... OK				Allocating navigation index table... OK
Allocating transformations... OK: #elems in alloc_mem=5, mem_	Allocating transformations... OK: #elems in alloc_mem=5, mem_
Allocating daughter lists... OK					Allocating daughter lists... OK
 geometry OK: #elems in alloc_mem=7, mem_map=38013, dau_gpu_c	 geometry OK: #elems in alloc_mem=7, mem_map=38013, dau_gpu_c
NUMBER OF PLACED VOLUMES 18789					NUMBER OF PLACED VOLUMES 18789
NUMBER OF UNPLACED VOLUMES 145					NUMBER OF UNPLACED VOLUMES 145
Copying geometry to GPU...					Copying geometry to GPU...

Copying logical volumes... OK;	TIME NEEDED 0.000615441s      |	Copying logical volumes... OK;	TIME NEEDED 0.000695619s
Copying unplaced volumes... OK;	TIME NEEDED 0.000503695s      |	Copying unplaced volumes... OK;	TIME NEEDED 0.000411785s
Copying transformations_... OK;	TIME NEEDED 0.00657207s       |	Copying transformations_... OK;	TIME NEEDED 0.0558993s
Copying placed volumes... OK;	TIME NEEDED 0.00866507s       |	Copying placed volumes... OK;	TIME NEEDED 0.0913828s
Copying daughter arrays... OK;	TIME NEEDED 0.00384211s       |	Copying daughter arrays... OK;	TIME NEEDED 0.00892739s
Geometry synchronized to GPU in 0.036591 s.		      |	Geometry synchronized to GPU in 0.173805 s.
     ---  InitElectronData ... 					     ---  InitElectronData ...
     ---  BuildELossTables ...					     ---  BuildELossTables ...
...								...
iter  221 -- tracks in flight:     2 energy deposition:    77	iter  221 -- tracks in flight:     2 energy deposition:    77
iter  222 -- tracks in flight:     0 energy deposition:    77	iter  222 -- tracks in flight:     0 energy deposition:    77
Run time: 0.0552					      |	Run time: 0.0532
```