[REFACTOR] Clean up chainladder.__init__.py

[genedan]

Description

Currently working on this, I was trying to clean up some repetitive code:

chainladder-python/chainladder/__init__.py

Lines 6 to 18 in 9e833f6

	_DT64_DTYPE = pd.to_datetime(["2000-01-01"]).dtype
	_ULT_VAL: str = str(
	pd.Timestamp("2262-01-01") - \
	pd.Timedelta(1, unit=np.datetime_data(_DT64_DTYPE)[0])
	)
	class Options:
	ARRAY_BACKEND = "numpy"
	AUTO_SPARSE = True
	ARRAY_PRIORITY = ["dask", "sparse", "cupy", "numpy"]
	ULT_VAL: str = _ULT_VAL
	DT64_UNIT: str = np.datetime_data(_DT64_DTYPE)[0]
	DT64_DTYPE: str = str(_DT64_DTYPE)

but this revealed other tasks that we'll have to address via multiple PRs. These would include but are not limited to:

• validation or deprecation of Options.get_option
• deprecation of auto_sparse and auto_backend
• add Options.reset_... for each option.

Is your feature request aligned with the scope of the package?

• Yes, absolutely!
• No, but it's still worth discussing.
• N/A (this request is not a codebase enhancement).

Describe the solution you'd like, or your current workaround.

I will reorganize Options with an init, and set the attributes to be assigned to the instance rather than class.

Do you have any additional supporting notes?

No response