Improve type annotations for core.(trajectory/units) (#3832)

* relocate dunder methods to top for core.trajectory

fix `core.operations`

add types for site, mypy errors to fix

remove no_type_check decorator

move dunder methods to the top

fix mypy errors

remove debug tag

improve `spectrum`

finish `core.tensors`

finish `xcfunc`

fix hash of `SymmOp`

finish `core.trajectory`

Add types for `core.molecular_orbitals/operations/sites/spectrum/tensor/xcfunc`  (#3829)

* fix `core.molecular_orbitals`

* fix `core.operations`

* add types for site, mypy errors to fix

* remove no_type_check decorator

* move dunder methods to the top

* fix mypy errors

* remove debug tag

* improve `spectrum`

* finish `core.tensors`

* finish `xcfunc`

* fix hash of `SymmOp`

* add a missing type

* Revert "fix hash of `SymmOp`"

This reverts commit bf2a953.

* fix some types in operations

* "TEST": remove one unused var, relocate another

* final tweak types

* avoid hard-code class name

* format tweaks

* type tweak

* fix unit test

* replace all `[0:x]` with `[:x]`

Guard `TYPE_CHECKING` only imports (#3827)

* flake8 --select=TYP001

* fix type import

* format docstring to google style

* fix more unguarded typecheck imports

* format more docs to Google format

* trigger CI (better var names)

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Co-authored-by: Janosh Riebesell <janosh.riebesell@gmail.com>

move structures out of util dir (#3831)

Add matgenb in the aux link section. Because apparently it is not
"discoverable". Fixes #3811.

More updates.

Move AIMS notebooks to matgenb.

Add README in examples folder that point to proper resources.

Improve type annotations and comments for `io.cif` (#3820)

* remove duplicate warning

* type and docstring tweaks

* add some types for io.cif

* add comments and types

* temp save of some formatting

* revert functional change

* revert unrelated changes

* fix unit test

* remove update that does nothing

* relocate `sub_space_group` and `space_groups` to their usage

* add more types

* pre-commit auto-fixes

* breaking: make parse_magmom/oxi_stats private

* remove merge header

* fix unit test

* add more types

* fix mypy errors

* add a few spaces

* remove if name ==main

* simplify "check to see if" in comments

* final tweaks

* revise docstring

* replace deprecated abc.abstractproperty

* add missing doc strings and standardize existing

* breaking: fix typo in method name orthongonalize_structure

* revert accidental change in test_composition.py

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Co-authored-by: Janosh Riebesell <janosh.riebesell@gmail.com>

* remove accidental change

* fix mypy errors

* fix mypy error

* add some for core.units

* rename `ArrayWithFloatWithUnit` to `ArrayWithUnit` in comment

* fix mypy errors

* tweak docstring for units

* nest internal funcs for units

* simplify module docstring

* revert to accessing private attrib

* fix unit test and revert support for `Unit`

* use `str` over `Unit`

* support unit as both str and Unit

* tweak docstring example

* improve IndexError messages

* test_index_error

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Co-authored-by: Janosh Riebesell <janosh.riebesell@gmail.com>