GH-48608: [Python] Fix interpolate actual values in Message.__repr__ f-string

[Aokizy2]

Rationale for this change

Message.__repr__ showed format placeholders ({self.type}) instead of actual values.

What changes are included in this PR?

Add missing f prefix to f-string in Message.__repr__ (pyarrow/lib.pxi).

Are these changes tested?

Yes: added test verifying string representation shows actual values.

Are there any user-facing changes?

Yes (bug fix): str(message) now shows values like type: RecordBatch instead of placeholders.
related to issue #48608

• GitHub Issue: [Python] ipc.Message __repr__ format string not applied #48608

[github-actions]

Thanks for opening a pull request!

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

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

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See also:

• Other pull requests
• Contribution Guidelines - Contributing Overview

[rustyconover]

@Aokizy2 looks great to me, please rename this PR to follow the recommended naming convention.

[github-actions]

⚠️ GitHub issue #48608 has been automatically assigned in GitHub to PR creator.

[Aokizy2]

@rustyconover OK,I've renamed this PR.

[rustyconover]

Looks great to me.

[rok]

Thanks finding this @rustyconover and for opening a PR @Aokizy2!
This is pretty straight forward and odd that it got looked over when it was added!
Would it be possible to add a test for this to prevent any future regressions?

[rustyconover]

I think the diff has too many formatting changes in it, can you have it not change so much existing code?

[Aokizy2]

sure,I'll change it

[Aokizy2]

Is it ok now?

[rok]

Thanks, that looks good @Aokizy2, will merge if CI passes.