[`flake8-bugbear`] Add `B912`: `map()` without an explicit `strict=` parameter (#20429)
## Summary
Implements new rule `B912` that requires the `strict=` argument for
`map(...)` calls with two or more iterables on Python 3.14+, following
the same pattern as `B905` for `zip()`.
Closes #20057
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Co-authored-by: dylwil3 <dylwil3@gmail.com>