build: enable clang-tidy misc-include-cleaner for include hygiene

[yadavay-amzn]

What

Closes #73. Enables clang-tidy's misc-include-cleaner check to enforce include hygiene.

How

Adds misc-include-cleaner to .clang-tidy. Because the project already runs clang-tidy 22 incrementally (changed-lines-only) via the cpp-linter workflow, include hygiene is now enforced on new/changed code with no additional tooling, workflow, or mapping file. IgnoreHeaders is configured for third-party headers (arrow, nanoarrow, nlohmann-json, spdlog, CRoaring, cpr) to suppress noise from vendored includes.

Notes

This supersedes the original IWYU-based approach (a separate workflow + iwyu.imp mapping + CMake option), per the review discussion with @zhjwpku: misc-include-cleaner integrates with the existing clang-tidy setup and is far lower-maintenance for the same goal.

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This contribution was authored with assistance from Claude Opus 4.8, in line with the Iceberg guidelines for AI-assisted contributions (https://iceberg.apache.org/contribute/#guidelines-for-ai-assisted-contributions). All changes were reviewed and tested by the author.

[zhjwpku]

Not too sure, but should we pursue LLVM include-cleaner [1]?

[1] https://clang.llvm.org/extra/clang-tidy/checks/misc/include-cleaner.html

[yadavay-amzn]

Good suggestion - pivoted to misc-include-cleaner. Since the project already runs clang-tidy 22 incrementally via cpp-linter, this enforces include hygiene on changed lines with no new tooling, so I dropped the separate IWYU workflow, iwyu.imp mapping, and CMake option. Added misc-include-cleaner.IgnoreHeaders for the vendored third-party headers (arrow, nanoarrow, nlohmann, spdlog, CRoaring, cpr) to suppress noise. The diff is now just a few lines in .clang-tidy. Updated the PR title/description accordingly.