GH-43301: [C++][Parquet] Enhance the comment for ColumnReader/Decoder

[mapleFU]

Rationale for this change

Enhance the comment for ColumnReader/Decoder

What changes are included in this PR?

Enhance the comment for ColumnReader/Decoder

Are these changes tested?

no need

Are there any user-facing changes?

no

• GitHub Issue: [C++][Parquet] Enhance the develop document for ColumnReader/Decoder #43301

[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}

In the case of PARQUET issues on JIRA the title also supports:

PARQUET-${JIRA_ISSUE_ID}: [${COMPONENT}] ${SUMMARY}

See also:

• Other pull requests
• Contribution Guidelines - Contributing Overview

[mapleFU]

@wgtmac @pitrou would you mind take a look? This just edit the comments

[mapleFU]

This is a logical change but I don't think it would matter 😅

[pitrou]

Sounds reasonable to me.

[pitrou]

LGTM except for a few suggestions

[mapleFU]

Would merge after ci pass

[conbench-apache-arrow]

After merging your PR, Conbench analyzed the 4 benchmarking runs that have been run so far on merge-commit cd50c32.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details. It also includes information about 102 possible false positives for unstable benchmarks that are known to sometimes produce them.