test(generators): the 5-second per-case DEADLINE in options.py fails CI on a stalled runner #1428

Describe the bug
examples/generators/options.py:154 sets DEADLINE = 5. _deadline (:1769-1793) arms signal.alarm around each case, and records the case as 'TIMEOUT' when the alarm fires. The 5s budget is a wall-clock limit with no scaling, so a stalled CI runner fails a case that takes milliseconds.

Evidence
Unit Tests run 37823543949 on main (a8cc02594), job 113470460900 (Python 3.14):

• The failure is SUBFAILED(type='2') tests/protocols/test_option_generator_httpv2_stream_unit.py::…::test_every_frame_type_is_generated - AssertionError: 'TIMEOUT' != 'OK', with the detail did not finish within 5s.
• The pytest output shows ~32s and ~26s gaps with no progress, and the job took 564.7s against 334–399s on the previous main run.
• Locally, all 10 HTTP/2 frame cases round-trip in 1.0–4.6ms (type 2: 1.32ms), ~3,800× under the budget.
• fix(pcapng)!: keep an SHB or IDB shorter than its fixed fields as captured (#1422) #1425 (the head) touched only pcapng.

Expected behavior
A case should not fail CI because the runner stalls. Options:

• read PCAPKIT_TEST_TIMEOUT_SCALE (the hook in tests/_support.py:25) when the generator runs under the tests
• raise the default budget
• or both

Blocked until #1427 merges, since it owns examples/generators/options.py in this wave.