Adding getters for other electronic integrals

[vaferreiQMT]

Is your feature request related to a problem? Please describe.
OPI currently has getters for some of the integrals available from ORCA such as get_int_hcore, get_int_overlap however it lacks similar getters for some of the other integrals, such as HMO, T and V as well as two electron integrals, which presumably could also be exposed to the user similarly.

Describe the solution you'd like
Additional getters in src/opi/output/core.py for other 1 electron integrals and 2 electron integrals, in a similar format to the existing getters.

Describe alternatives you've considered
As an alternative it is possible to directly extract this information from the GBW JSON data, however this negates the nice and safe getters introduced in OPI.

Additional context
I'm not sure if there is a particular reason why these other integrals might not be implemented yet, but if it is simply a matter of not having gotten round to it quite yet, I would also be happy to make a PR following in the form of the other getters, which you can then tweak as you find suitable.

Thanks for your time!

[haneug]

Thank you for raising this issue! There is no particular reason why we did not add these integrals yet. We just did not come to it. We planned to generally clean up the getters for the integrals (see #207) and would like in the future the option to change the phase factors and order of the angular momentums (for different conventions) but there are no concrete plans yet.

So we would be happy to receive a PR from you that implements these additional integrals like the ones we already have!