Preserve abstract signatures without runtime when translation is disabled

[Morriar]

When translate_abstract_methods is false, abstract signatures should remain unchanged. Previously, the translator emitted member annotations before deciding to skip the signature, adding a stray # @without_runtime above T::Sig::WithoutRuntime.sig.

Filter skipped abstract signatures before generating annotations or rewriting methods. Concrete signatures continue to translate normally.

For this input:

T::Sig::WithoutRuntime.sig do
  abstract.params(query: Collect::PrivateAssociationRelation).returns(T::Array[T.attached_class])
end
def collect(query); end

Before: translation adds an annotation even though the signature is skipped.

# @without_runtime
T::Sig::WithoutRuntime.sig do
  abstract.params(query: Collect::PrivateAssociationRelation).returns(T::Array[T.attached_class])
end
def collect(query); end

After: the signature and method remain unchanged.

T::Sig::WithoutRuntime.sig do
  abstract.params(query: Collect::PrivateAssociationRelation).returns(T::Array[T.attached_class])
end
def collect(query); end