TST: require expected_warning and match in assert_produces_warning

[jbrockmendel]

Follow-up to GH-67275, taking up @mroeschke's suggestion there: instead of a pre-commit check, enforce the message assertion in the signature of assert_produces_warning itself.

• expected_warning becomes a required positional. Dropping its Warning default removes a footgun the lint check did not address at all: assert_produces_warning(match="...") previously accepted any warning class.
• match defaults to lib.no_default; passing a truthy expected_warning without it raises TypeError. match=None remains the opt-out, the same spelling the lint check accepted.
• maybe_produces_warning takes match as a required keyword-only argument, so the condition=False branch is covered too.

Making match unconditionally required was the other option, but it would mean adding a meaningless match=None to the 221 assert_produces_warning(None) / (False) calls, which assert that nothing is warned and so have no message to match. The sentinel keeps those untouched.

This supersedes the bare_assert_produces_warning check, which is removed here along with its pre-commit hook and script tests. The signature covers every call site in the repo rather than just pandas/tests/, sees through variables (the static check needed a hand-written exemption for a parametrized false_or_none), and needs no maintained script. The one thing it gives up is a bare call in a test that never runs in any CI job.

An AST sweep of the whole repo found 48 calls relying on the old Warning default, all in pandas/tests/interchange/; those now name Pandas4Warning explicitly. No call anywhere passed a truthy expected_warning without match — GH-67275 had already fixed those — so there is no other call-site churn.

Full pandas/tests run is green (244207 passed, 8486 skipped, 1510 xfailed) and pre-commit run --all-files passes with no files modified.

AI disclosure: drafted with Claude Code (claude opus 5 (high)), which prototyped the signature change, ran the AST sweep over call sites, and ran the test suite and pre-commit.

[mroeschke]

Thanks @jbrockmendel