[flake8-bugbear] Make B911 example error out-of-the-box (#19051)

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## Summary

<!-- What's the purpose of the change? What does it do, and why? -->

Part of #18972

This PR makes [batched-without-explicit-strict
(B911)](https://docs.astral.sh/ruff/rules/batched-without-explicit-strict/#batched-without-explicit-strict-b911)'s
example error out-of-the-box

[Old example](https://play.ruff.rs/a897d96b-0749-4291-8a62-dfd4caf290a0)
```py
itertools.batched(iterable, n)
```

[New example](https://play.ruff.rs/1c1e0ab7-014c-4dc2-abed-c2cb6cd01f70)
```py
import itertools

itertools.batched(iterable, n)
```

Imports were also added to the "use instead" sections

## Test Plan

<!-- How was it tested? -->

N/A, no functionality/tests affected

crates/ruff_linter/src/rules/flake8_bugbear/rules/batched_without_explicit_strict.rs

@@ -20,16 +20,22 @@ use crate::{FixAvailability, Violation};
 ///
 /// ## Example
 /// ```python
+/// import itertools
+///
 /// itertools.batched(iterable, n)
 /// ```
 ///
 /// Use instead if the batches must be of uniform length:
 /// ```python
+/// import itertools
+///
 /// itertools.batched(iterable, n, strict=True)
 /// ```
 ///
 /// Or if the batches can be of non-uniform length:
 /// ```python
+/// import itertools
+///
 /// itertools.batched(iterable, n, strict=False)
 /// ```
 ///