feat: deterministic metadata encoding

[timsaucer]

Which issue does this PR close?

• Closes Deterministic metadata encoding #7448

Rationale for this change

The ordering of metadata is not consistent since it uses a HashMap. It can be useful in unit tests to verify an output from a known hash of it's serialized values. With metadata this is not consistent.

What changes are included in this PR?

Adds ordering to the hashmap keys when encoding.

Are there any user-facing changes?

No.

Example

If you run this example multiple times, you will see the encoding changes from run to run based on the non-deterministic ordering of the hashmap iterator.

use std::{hash::Hasher, sync::Arc};

use arrow::{array::RecordBatch, datatypes::Schema};

fn main() {
    let schema = Arc::new(
        Schema::empty().with_metadata(
            [
                ("a".to_owned(), "1".to_owned()), //
                ("b".to_owned(), "2".to_owned()), //
                ("c".to_owned(), "3".to_owned()), //
                ("d".to_owned(), "4".to_owned()), //
                ("e".to_owned(), "5".to_owned()), //
            ]
            .into_iter()
            .collect(),
        ),
    );
    let batch = RecordBatch::new_empty(schema.clone());

    dbg!(&batch.schema().metadata().keys());

    let mut bytes = Vec::new();
    let mut w = arrow::ipc::writer::StreamWriter::try_new(&mut bytes, &schema).unwrap();
    w.write(&batch).unwrap();
    w.finish().unwrap();

    let mut h = std::hash::DefaultHasher::new();
    h.write(&bytes);
    let h = h.finish();

    eprintln!("{} bytes -- h = {h:x}", bytes.len());
}

[timsaucer]

I currently based this off 54.3.1 but I will updated it to main after we have completed internal testing.

[timsaucer]

Rebased on main, ready for review.

[alamb]

Thanks @timsaucer -- I think this PR makes sense to me

Can you please file a ticket (it makes for better release notes / easier to understand what changed)

[timsaucer]

@alamb Thank you for the review. I have added an issue as requested, but as I am not a committer on arrow-rs I will need someone else to merge this.

[alamb]

@alamb Thank you for the review. I have added an issue as requested, but as I am not a committer on arrow-rs I will need someone else to merge this.

I will merge it in a day or two to give others a chance to comment if they desire.

FYI @etseidl and @tustvold

[alamb]

Thanks again @timsaucer and @etseidl