[09Catho]

Rationale for this change

parquet/level_comparison.h is only included by Parquet implementation files, but Meson installs it with the public Parquet headers. Renaming it as an internal header makes that boundary explicit and prevents it from being treated as public API.

What changes are included in this PR?

• Rename level_comparison.h to level_comparison_internal.h.
• Update the eight internal include sites.
• Remove the header from Meson's installed-header list.

This addresses #55455 without changing runtime behavior.

Are these changes tested?

• git diff --check passed.
• Repository-wide search found no remaining parquet/level_comparison.h include or install reference.
• A narrow CMake configure reached Arrow's bundled Boost dependency setup, but could not complete within the local validation window; no C++ build result is claimed.

Are there any user-facing changes?

The header is no longer installed as a public Parquet header. No runtime behavior changes.

Was AI used for this PR?

In accordance with the Arrow AI-generation guidance:

PR code and description written by:

• Human
• AI

Reviewed before submission by:

• Human
• AI
• Not reviewed

Codex was used to inspect the issue, implement the scoped rename, and prepare this description. The complete diff was reviewed in this run, and the validation limits are stated above.

• GitHub Issue: [C++][Parquet] Make parquet/level_comparison.h internal #55455

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[github-actions]

⚠️ GitHub issue #55455 has been automatically assigned in GitHub to PR creator.