fix a bug in add two bond lists.

[0ut0fcontrol]

after adding two bond list, merged_bond_list has wrong _max_bonds_per_atom.

import numpy as np
import biotite.structure as struc
bond_list1 = struc.BondList(2, np.array([(0,1)])) # max_bond_per_atom=1
bond_list2 = struc.BondList(3, np.array([(0,1),(0,2)])) # max_bond_per_atom=2
added_list = bond_list1 + bond_list2

print(f"{added_list._max_bonds_per_atom=}")

bonds, types = added_list.get_bonds(2)
print(f"{bonds.tolist()=} {types.tolist()=}")

print(f"{added_list.as_array().tolist()=}")

# output values:
# added_list._max_bonds_per_atom=1   (wrong, expected value is 2)
# bonds.tolist()=[3] types.tolist()=[0] (wrong, expect 2 bonds)
# added_list.as_array().tolist()=[[0, 1, 0], [2, 3, 0], [2, 4, 0]] (right)

[padix-key]

Nice find! This is definitely a typo from my side.

This looks ready to merge from my side, but with the new PR policy of the new governance I will leave the PR open for 48 hours.