Add ASE ingester and generalize other ingestion utilities

[ml-evs]

This PR adds from_ase as a new ingester type (following #1296 for pymatgen) and generalises the ingester functionality into a .ingest_from method of the base adapter, e.g.,

from optimade.adapters import Structure

atoms = ase.Atoms(...)
structure = pymatgen.core.Structure(...)

Structure.ingest_from(atoms)  # implicit type detection
Structure.ingest_from(structure)  # implicit type detection
Structure.ingest_from(atoms, "ase")  # use key into ingester dict to specify
Structure.ingest_from(pymatgen, "pymatgen")  # use key into ingester dict to specify

Also adds several utilities for e.g., normalizing formulae and other fields. These are now used in the adapters and spread across various utils modules (to avoid circular imports).

[codecov]

Codecov Report

Merging #1509 (baf4799) into master (7c8f9a6) will increase coverage by 0.06%.
The diff coverage is 94.38%.

@@            Coverage Diff             @@
##           master    #1509      +/-   ##
==========================================
+ Coverage   90.95%   91.01%   +0.06%     
==========================================
  Files          74       74              
  Lines        4411     4475      +64     
==========================================
+ Hits         4012     4073      +61     
- Misses        399      402       +3     

Flag	Coverage Δ
project	91.01% <94.38%> (+0.06%)	⬆️
validator	90.36% <94.38%> (+0.07%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
optimade/adapters/base.py	96.96% <83.33%> (-3.04%)	⬇️
optimade/models/utils.py	92.50% <91.66%> (-0.29%)	⬇️
optimade/adapters/structures/ase.py	98.63% <97.36%> (-1.37%)	⬇️
optimade/adapters/structures/adapter.py	100.00% <100.00%> (ø)
optimade/adapters/structures/pymatgen.py	98.50% <100.00%> (-0.16%)	⬇️
optimade/adapters/structures/utils.py	80.74% <100.00%> (+0.74%)	⬆️
optimade/models/structures.py	96.42% <100.00%> (+0.67%)	⬆️

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[ml-evs]

Hi @JPBergsma, will merge this tomorrow, let me know if you want to have a second look first and I'll hold off.

[JPBergsma]

I had a quick look and everything seems OK.