Forbid uppercased propositions in LDLf

[marfvr]

Is your feature request related to a problem? Please describe.
Currently, it is still legal to create an LDLf formula whose atoms have upper-cased characters, differently from LTLf.

from flloat.parser.ltlf import LTLfParser
LTLfParser()("F(a)") # this is OK
LTLfParser()("F(A)") # this raises error

from flloat.parser.ldlf import LDLfParser
LTLfParser()("a") # this is OK
LTLfParser()("A") # this is OK although should raise exception

Describe the solution you'd like
Update LDLf module to forbid uppercased propositions.

Describe alternatives you've considered

Additional context

[cipollone]

Yes, this was the intended behaviour.
The naming convention for all atomics is:

flloat/flloat/base.py

Lines 33 to 41 in 75e8ec9

	class AtomicFormula(Formula, ABC):
	"""An abstract atomic formula.
	Both formulae and names can be used as atomic symbols.
	A name must be a string made of letters, numbers, underscores, or it must
	be a quoted string.
	"""
	name_regex = re.compile(r'(\w+)|(".*")')

This is inherited by PLAtomic and LDLfPropositionalAtom. Instead, LTLfAtomic overrides the regex to forbid uppercase letters (to solve the ambiguity with with temporal operators).

Maybe we prefer a more uniform behaviour, among logics. In this case, we can simply move the regex from LTLfAtomic to AtomicFormula, to apply it to all of them.