Implement Hash for Schema

[crepererum]

Which issue does this PR close?

Closes #2182.

Rationale for this change

Hash is sometimes helpful, see #2182 for some examples.

What changes are included in this PR?

Implements Hash for Schema.

Are there any user-facing changes?

New trait implementation, not a breaking change.

[tustvold]

I think this is fine, although I do wonder if we need some way to highlight that this is a relatively expensive computation...

[crepererum]

I think this is fine, although I do wonder if we need some way to highlight that this is a relatively expensive computation...

The "expensiveness" was more concerned regarding the usage. I think a user should judge how expensive Eq/Hash on complex/container-like data structures are. You can easily Eq/Hash BTreeSet<BTreeMap<String, Vec<String>>> but sure, it's expensive. Same goes for a Schema, esp. if you attach LOADS for metadata.

However we could add a doc comment somewhere.

[ursabot]

Benchmark runs are scheduled for baseline = b8e034c and contender = 6c77cd5. 6c77cd5 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