Deprecated the public expose of test_util package

[klion26]

Which issue does this PR close?

Closes #7294.

Rationale for this change

What changes are included in this PR?

Same as the issue

Are there any user-facing changes?

No

[klion26]

@alamb Please have a look at this when you're free, thanks.

[alamb]

Thanks @klion26 -- this looks good though it looks like there are some clippy failures (as the code is still used internally). Is there any chance you can help fix the CI?

[klion26]

@alamb Thanks for the review. I will take a look at the Clippy failures soon.

[klion26]

@alamb Before making the change, could you please help to check something below, thanks.

1. The tests in arrow/src/util/test_util.rs will show that it uses deprecated code when doing clippy, do I need to add #[allow(deprecated)] before the function pub fn seedable_rng() (after removing all the outside usage)
2. When removing the usage of the function in arrow/src/util/test_util.rs(seedable_rng, parquet_test_data, and arrow_test_data), we can copy the code from arrow/src/util/test_util.rs to the other place, is this understanding right? if not, what else do I need to do
3. After removing the outside usage, do we need to remove the dead function for now, or we can do it in a follow pr.

[alamb]

@alamb Before making the change, could you please help to check something below, thanks.

1. The tests in arrow/src/util/test_util.rs will show that it uses deprecated code when doing clippy, do I need to add #[allow(deprecated)] before the function pub fn seedable_rng() (after removing all the outside usage)
2. When removing the usage of the function in arrow/src/util/test_util.rs(seedable_rng, parquet_test_data, and arrow_test_data), we can copy the code from arrow/src/util/test_util.rs to the other place, is this understanding right? if not, what else do I need to do
3. After removing the outside usage, do we need to remove the dead function for now, or we can do it in a follow pr.

I recommend doing the [allow(deprecated)] route -- and when we are ready to actually remove the deprecated API (per guideliens here https://github.com/apache/arrow-rs?tab=readme-ov-file#rust-version-compatibility-policy) then we can copy / move the code elsewhre

[klion26]

There is some warnings for the test function in test_util.rs after adding #[allow(deprecated)], will figure out how to fix it and come back.

[klion26]

I added this here because it will always throw the error after I try adding #[allow(deprecated)] before mode tests, use supper::*, and the function name fn test_data_dir(), fn test_happy().

[klion26]

@alamb, could you please look at this when you're free? thanks.