fix(foundation): third-party engines replace a user's verbose callback with their own printer #1874

Extractor.__init__ sets _flag_v = True and stores the callable when verbose is one (pcapkit/foundation/extraction.py:1293-1295). But each third-party engine then does if ext._flag_v: ext._vfunc = lambda e, f: print(...). That happens in foundation/engines/scapy.py:387-391, dpkt.py:~461, pyshark.py:~262, pypcap.py:~319, pcap_ct.py:~406 and pypcapfile.py:~227. So on those engines a user's own verbose= callback is silently replaced by the engine's print. Only the built-in PCAP and PCAP-NG engines keep it.

Found while typing _vfunc for #1839 (#1867).

Fix: install an engine's default printer only when verbose=True was passed as a bool, and keep a user callable as given. The test should run a non-default engine with a recording callback and assert the callback is called for every frame.