fix(neutron): refactor palo_alto to move pure functions out of class

[nidzrai]

What does this change do?

1. These methods don't use self except to get their inputs , so moving out these pure functions to module level
2. Added named exception
3. One router-lookup helper
4. redundant _has_subport , removed dead _remove_gateway_subport
5. change _ensure_parent_vif_attached a single exit path (Fetch the port, check Ironic annotated it, return it" lived in both the helper and the main function) , _confirm_parent_vif_attach_after_error returned dict but ideally it should be bool .
6. Refactor _InterfaceAttachment checks, moved th check out of handler
7. Move the gateway/interface wiring methods (anchor network, parent port, VIF attach, trunk, subports, teardown, snapshot/undo) from the PaloAlto L3 service provider into a PaloAltoWiring class in palo_alto_wiring.py. The class has no callback subscriptions, so the planned wiring reconciler can reuse it outside the L3 plugin.

This is a move only: method names and bodies are unchanged, except that the Ironic client and trunk plugin lookups are now methods instead of properties. PaloAlto keeps the event subscriptions, flavor check, node adopt/release and rollback bookkeeping, and delegates wiring to self._wiring. It still creates the IronicClient and passesthe wiring a getter, so both share one lazily created client.

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