Use required-features for CSV benchmarks/examples

[tustvold]

Which issue does this PR close?

Closes #.

Rationale for this change

Makes the code easier to understand, and avoid unused code warnings when compiling with --no-default-features

What changes are included in this PR?

Are there any user-facing changes?

[alamb]

👍 Nice cleanup

Note to other reviewers I found whitespace blind diff https://github.com/apache/arrow-rs/pull/2602/files?diff=split&w=1 easier to review

[ursabot]

Benchmark runs are scheduled for baseline = 12ad8d7 and contender = 20282d1. 20282d1 is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ec2-t3-xlarge-us-east-2] ec2-t3-xlarge-us-east-2
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on test-mac-arm] test-mac-arm
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ursa-i9-9960x] ursa-i9-9960x
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ursa-thinkcentre-m75q] ursa-thinkcentre-m75q
Buildkite builds:
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java