Apply clang-format to whole codebase

[ThisIsFineTM]

The formatting is a little inconsistent from file to file. We have a clang-format config present in the repo already: https://github.com/openzim/zim-tools/blob/main/.clang-format

Could we run clang-format on everything? I can also add precommit hooks in contrib that developers could opt-in to for automatically running clang-format.