Update half requirement from 1.8 to 2.0 (apache#1919)

Updates the requirements on [half](https://github.com/starkat99/half-rs) to permit the latest version.
- [Release notes](https://github.com/starkat99/half-rs/releases)
- [Changelog](https://github.com/starkat99/half-rs/blob/main/CHANGELOG.md)
- [Commits](starkat99/half-rs@v1.8.0...v2.0.0)

---
updated-dependencies:
- dependency-name: half
  dependency-type: direct:production
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

arrow/Cargo.toml

@@ -44,7 +44,7 @@ serde_json = { version = "1.0", default-features = false, features = ["preserve_
 indexmap = { version = "1.6", default-features = false, features = ["std"] }
 rand = { version = "0.8", default-features = false, features =  ["std", "std_rng"], optional = true }
 num = { version = "0.4", default-features = false, features = ["std"] }
-half = { version = "1.8", default-features = false }
+half = { version = "2.0", default-features = false }
 csv_crate = { version = "1.1", default-features = false, optional = true, package="csv" }
 regex = { version = "1.5.6", default-features = false, features = ["std", "unicode"] }
 lazy_static = { version = "1.4", default-features = false }