fix initial MCMC values

[johannesostner]

Fixes initialization of MCMC values (pyro-ppl/numpyro#1604)

PR Checklist

• Referenced issue is linked
• If you've fixed a bug or added code that should be tested, add tests!
• Documentation in docs is updated

Description of changes

Fixes initialization of MCMC values (pyro-ppl/numpyro#1604)

Technical details

numpyro 0.12 changed the way init_params is handled in MCMC (see pyro-ppl/numpyro#1604). This fix reflects these changes in pertpy

[Zethson]

mypy:

mypy.....................................................................Failed
- hook id: mypy
- exit code: 1

pertpy/tools/_coda/_tasccoda.py: note: In member "set_init_mcmc_states" of class "Tasccoda":
pertpy/tools/_coda/_tasccoda.py:308:5: error: Signature of
"set_init_mcmc_states" incompatible with supertype "CompositionalModel2" 
[override]
        def set_init_mcmc_states(self, rng_key: None, ref_index: np.ndarra...
        ^
pertpy/tools/_coda/_tasccoda.py:308:5: note:      Superclass:
pertpy/tools/_coda/_tasccoda.py:308:5: note:          def set_init_mcmc_states(self, *args: Any, **kwargs: Any) -> Any
pertpy/tools/_coda/_tasccoda.py:308:5: note:      Subclass:
pertpy/tools/_coda/_tasccoda.py:308:5: note:          def set_init_mcmc_states(self, rng_key: None, ref_index: Any, sample_adata: Any) -> Any
pertpy/tools/_coda/_sccoda.py: note: In member "set_init_mcmc_states" of class "Sccoda":
pertpy/tools/_coda/_sccoda.py:196:5: error: Signature of "set_init_mcmc_states"
incompatible with supertype "CompositionalModel2"  [override]
        def set_init_mcmc_states(self, rng_key: None, ref_index: np.ndarra...
        ^
pertpy/tools/_coda/_sccoda.py:196:5: note:      Superclass:
pertpy/tools/_coda/_sccoda.py:196:5: note:          def set_init_mcmc_states(self, *args: Any, **kwargs: Any) -> Any
pertpy/tools/_coda/_sccoda.py:196:5: note:      Subclass:
pertpy/tools/_coda/_sccoda.py:196:5: note:          def set_init_mcmc_states(self, rng_key: None, ref_index: Any, sample_adata: Any) -> Any
Found 2 errors in 2 files (checked 57 source files)

and flake8

pertpy/tools/_coda/_base_coda.py:294:104: B026 Star-arg unpacking after a keyword argument is strongly discouraged, because it only works when the keyword parameter is declared after all parameters supplied by the unpacked sequence, and this change of ordering can surprise and mislead readers.
pertpy/tools/_coda/_base_coda.py:348:102: B026 Star-arg unpacking after a keyword argument is strongly discouraged, because it only works when the keyword parameter is declared after all parameters supplied by the unpacked sequence, and this change of ordering can surprise and mislead readers.