fix(reassembly): Deferred cannot be pickled under protocol 0 or 1 #2423

Describe the bug

Deferred (pcapkit/foundation/reassembly/data/data.py) declares __slots__ with no __getstate__/__setstate__, so it cannot be pickled under pickle protocols 0 or 1 at all — this is independent of the AppType/EnumRegistry pickle fix landing in #2421 and reproduces for any Deferred instance, including a bare Deferred(..., 42, b'x') holding a plain int.

To Reproduce

import pickle
from pcapkit.foundation.reassembly.data.data import Deferred
d = Deferred(lambda p, b: None, 42, b'x')
pickle.dumps(d, protocol=0)  # or protocol=1

Expected behavior

Either Deferred gets a __getstate__/__setstate__ pair compatible with __slots__ (the standard pattern), or the class documents that it requires protocol 2+ (Python's default since 3.0, so likely low real-world impact, but worth stating explicitly if not fixed).

Additional context

Found during review of #2421 (AppType reassembly ports). Protocols 2–5 work correctly. Scoped out of that PR since it's a pre-existing gap, not something #2421 introduced.