Radioactivedecay

- Fix bug where the conversion of dpm to other activity units, and vice versa, was incorrect (87 &
88).

- Added support for Python v3.11. Use latest importlib-resources API (`files()` etc.) to fix
warnings. Fix pylint `__repr__()` usage warnings in tests. Use isort to sort imports and check in
code formatting action (85).

- Fix normal precision inventory unit tests for `decay()` and `cumulative_decays()` methods (84).
The tests now warn if the calculated floats are not exact matches for the test defaults, and assert
that the calculated floats are within max(rel_tol=1e-7, abs_tol=1e-30) of the expected values. This
means the tests that had previously started flaking on GitHub Actions CI (sporadically) will now
pass.

- Fix bug where high-precision (SymPy) default dataset had incorrect half-lives for Th-232, Sm-147
and Rb-87 (82). All users performing `InventoryHP` decay calculations for chains containing these
radionuclide are encouraged to upgrade without delay. Previous radioactivedecay versions gave
incorrect results (note normal precision `Inventory` decays were unaffected).

- Code improvement to support metastable states up to 6th state (76).
- Added labels for more decay modes (including heavy cluster decay modes) to decay chain plots code
(77).
- Improve parsing of nuclide strings (78). Note: you must use the correct capitalization of the
metastable state and the element chars when using mass number first format, e.g. use '130nI' to get
I-130n, not '130ni', '130Ni' or '130NI' as these will be mistaken as Nickel (Ni). Capitalization
does not matter if using element first formats, e.g. 'I-130N' or 'I130N' will be correctly parsed
to I-130n.

- Added more stable products to the default ICRP-107 dataset (75).