GH-32381: [C++] Improve error handling for hash table merges

[kris-gaudel]

Rationale for this change

Fixes #32381

What changes are included in this PR?

Proper error handling in util/hashing.h and unit test for said error handling in util/hashing_test.cc

Are these changes tested?

Yes, via included unit test

Are there any user-facing changes?

Yes, error handling in hashing utilities

• GitHub Issue: [C++] Improve error handling for hash table merges #32381

[github-actions]

Thanks for opening a pull request!

If this is not a minor PR. Could you open an issue for this pull request on GitHub? https://github.com/apache/arrow/issues/new/choose

Opening GitHub issues ahead of time contributes to the Openness of the Apache Arrow project.

Then could you also rename the pull request title in the following format?

GH-${GITHUB_ISSUE_ID}: [${COMPONENT}] ${SUMMARY}

or

MINOR: [${COMPONENT}] ${SUMMARY}

See also:

• Other pull requests
• Contribution Guidelines - Contributing Overview

[zanmato1984]

Thanks — the fix direction looks right to me overall, but I think there are two follow-ups worth addressing inline.