Addition

DFTB+ calculator that supports ES tracking
Davidson algorithm to converge normal modes after TS optimization. Allows verifying the nature/order of the saddle point, without explicit Hessian calculation (do_davidson: True). See examples/tsopt/04_diels_alder_xtb_tsopt_davidson for an example.
New, faster algorithms to detect bonds and bends in large(r) systems. Dihedral detection is yet to be updated and still slow for big systems.
More finegrained control over preconditioner construction, selectable via kind: full|full_fast|bonds_bends|bonds
- full/full_fast: Use bonds, bends, dihedrals
- bonds_bends: Use bonds and bends
- bonds: Only bonds.
Preconditioner construction was vastly accelerated.
Backtracking line search that also uses gradient information. Useful for XTB calculations, as the gradient is always available with the energy
Support for (re)using GFN-FF topology files in the XTB calculator
Nix installation using cached binaries, thanks to Cachix and @sheepforce. See the documentation on how to set up binary caching.

Bugfixes

Updated code to work with recently released h5py 3.0.0
pysisplot -o crash when no rendered CDDs were available
Handling of TS-optimization after COS optimization when HEI is first or last image
Line search now checks for very small alphas and aborts if necessary