chore(deps): Update half to 2.7.1, ignore RUSTSEC-2025-0111 (#18287)

## Which issue does this PR close?

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- Closes #18288

## Rationale for this change

`cargo audit` says that the current version of `half` we have in our
Cargo.lock file was yanked




```
Crate:     half
Version:   2.7.0
Warning:   yanked
Dependency tree:
half 2.7.0
```

And indeed it is:
https://crates.io/crates/half/versions
<img width="1193" height="830" alt="Screenshot 2025-10-26 at 7 20 54 AM"
src="https://github.com/user-attachments/assets/ad6944c6-912c-4c56-9d1d-efe760ae85ee"
/>

So let's update to a non yanked version

## What changes are included in this PR?

run `cargo update -p half` and check the result in

## Are these changes tested?

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## Are there any user-facing changes?

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Author: alamb

.github/workflows/audit.yml

@@ -46,4 +46,9 @@ jobs:
         with:
           tool: cargo-audit
       - name: Run audit check
-        run: cargo audit
+        # RUSTSEC-2025-0111: tokio-tar is by testcontainers for orchestration
+        # of testing, so does not impact DataFusion's security
+        # See https://github.com/apache/datafusion/issues/18288
+        # NOTE: can remove this once testcontainers releases a version that includes
+        # https://github.com/testcontainers/testcontainers-rs/pull/852
+        run: cargo audit --ignore RUSTSEC-2025-0111