Add wrapping and scaling methods to class Box

[PhilLecl]

See #11

This adds methods for converting wrapped/unwrapped and scaled/real coordinates.

I also have a (rudimentary) implementation for reading dumps with scaled and/or unwrapped coordinates at https://github.com/PhilLecl/lammpsio/tree/read-dump-su.
I've used it together with the dumps generated by the input script below to test the calculations.
Note that unwrapping can cause the floating point error to become rather large.

---

# randomly generated periodic triclinic simulation box
units real
region r1 prism -87 9 -80 58 -63 83 9 -13 5
boundary p p p
create_box 1 r1
mass * 1

# some random atoms with random velocities
create_atoms 1 random 100 20240519 NULL
velocity all create 298.15 20240519
fix thermostat all nvt temp 298.15 298.15 100.0

# dumps
dump d1 all custom 1000 dump.position_i id x y z ix iy iz
dump d2 all custom 1000 dump.position_u id xu yu zu
dump d3 all custom 1000 dump.position_si id xs ys zs ix iy iz
dump d4 all custom 1000 dump.position_su id xsu ysu zsu

# run
run 100000

[mphoward]

Thank you! This will be a nice feature to have available, and we will work to add some tests for it soon.

I would also welcome a pull request to support reading from / writing to scaled or unwrapped coordinates when you are ready. Could you open an issue so we can discuss that before you do so? I'd like to discuss a plan for that first, particularly whether multiple of those are allowed to be in a dump file and how lammpsio will transform them when they're read in.