De-duplicate `needs_strict_codec` between `tests/conftest.py` and `tests/test_verify.py`

Compare tests/conftest.py:65 with the local definition and helper at tests/test_verify.py:56-59. Remove the duplicate and use the shared definition as the other affected test files do, preserving the CI-context comment with the shared definition. Run the affected tests with -rs and confirm they execute rather than become skipped.

needs_strict_codec now exists twice in the test tree: the shared copy in tests/conftest.py and a local one in tests/test_verify.py.

State

The marker skips a test when the host codec can decode byte 0xff — every ISO-8859-x and cp125x codec maps all 256 byte values, so under such a locale a strict-decode test goes vacuously green rather than exercising the fault it is named for.

• tests/conftest.py:65 — the shared copy, added by the #380/#383 bundle so phase 2's tests could import it. Used by tests/test_multiplexer.py, tests/test_hook_bus.py and tests/test_probe.py.
• tests/test_verify.py:59 — a local copy predating it, with its own _codec_rejects_bad_byte helper. Used at :296, :1090 and :1114.

The two are byte-identical in condition and skip reason.

Why the duplication was left in place

test_verify.py is otherwise untouched by the #380/#383 fix. De-duplicating it would have dragged a large, unrelated file into a bundled fix whose whole discipline was to claim exactly what it fixed and no more. Deliberate, and named in that PR's "Out of scope" section — filed here so it does not simply rot.

Asked for

Delete the local copy and its _codec_rejects_bad_byte helper from tests/test_verify.py; import the shared one from conftest, as the other three files do.

Worth carrying over rather than dropping: the comment above the local copy (tests/test_verify.py:56-58) records that CI is always on the exercising side of this skip — the Linux legs run UTF-8 and the Windows legs set PYTHONUTF8=1 (.github/workflows/ci.yml). That fact belongs with the shared definition, which currently does not state it.

Verification

Mechanical, but confirm the tests still run rather than newly skipping — a marker refactor that silently flips three tests to skipped is indistinguishable from green. -rs on the affected file, or an explicit assertion on the collected outcome, is enough.