Replace object type comparisons with string comparisons when pandas dtype is of type string

[genedan]

Pandas now uses a default string type when it used to default to object type.

https://pandas.pydata.org/docs/dev/whatsnew/v3.0.0.html#dedicated-string-data-type-by-default

This will cause existing code that checks for type object to fail, such as line 424 in _drop_func:

chainladder-python/chainladder/development/base.py

Lines 414 to 436 in 6ea3577

	def _drop_func(self, factor):
	# get the appropriate backend for nan_triangle and nan_to_num
	xp = factor.get_array_module()
	# turn single drop_valuation parameter to list if necessary
	drop_list = self.drop if isinstance(self.drop, list) else [self.drop]
	# get an starting array of weights
	arr = factor.nan_triangle.copy()
	# accommodate ldf triangle as factor, where the dimensions are '12-24'
	dev_list = (
	factor.development.str.split("-", expand=True)[0]
	if factor.development.dtype == object
	else factor.development.astype("string")
	)
	# create ndarray of drop_list for further operation in numpy
	drop_np = np.asarray(drop_list)
	# find indices of drop_np
	origin_ind = np.where(
	np.array([factor.origin.astype("string")]) == drop_np[:, [0]]
	)[1]
	dev_ind = np.where(np.array([dev_list]) == drop_np[:, [1]])[1]
	# set weight of dropped factors to 0
	arr[(origin_ind, dev_ind)] = 0
	return xp.nan_to_num(arr)[None, None]

As far as I can tell, this is the only place in the package where this happens and causes test failures.