SLBFee.fxRateToBase is string, where all other fxRates are using Decimal

[debegr92]

fxRateToBase is used by a lot of entries in the Flex Query. It is always a decimal string and therefore handled as Decimal.
For SLBFee, the fxRateToBase is successfully parsed as string.

ibflex/ibflex/Types.py

Lines 2055 to 2062 in f1b96e2

	class SLBFee:
	"""Wrapped in <SLBFees>"""
	accountId: str | None = None
	acctAlias: str | None = None
	model: str | None = None
	currency: str | None = None
	fxRateToBase: str | None = None

This should be changed to use Decimal class as well.