Fix CI build warnings

[wgtmac]

There are a lot of CI warnings that are worth fixing. For example: https://github.com/apache/iceberg-cpp/actions/runs/19386197700/job/55473420291?pr=320

[Jinchul81]

I am interested in this work as a newcomer. May I provide a PR?

[Fokko]

@Jinchul81 Go ahead, first come, first serve :)

[Jinchul81]

Please review the PR #328

[Joe-Abraham]

I've created a PR to resolve the build warnings reported here. The fixes have been split into logical commits to make the review process easier:

1. Fixed unused parameter warnings: Added [[maybe_unused]] where appropriate.
2. Fixed uninitialized member warnings: Added default initializers to struct and class members.
3. Fixed integer sign comparison warnings: Used <utility> functions like std::cmp_equal, std::cmp_less.
4. Fixed various other build warnings: Addressed specific operator precedence warnings and redundant std::move calls.
5. Cleaned up shadowing warnings/unused functions: Renamed shadowed arguments and removed unused local test helpers.

PR Link - #587

@Fokko @wgtmac could some one help review and merge