Refactor and remove mwapi_errors

Merged Legoktm requested to merge error-refactor into main

Each crate now has its own error type that is the subset of mwapi_errors needed for that library.

Along the way we remove mwapi's unstable-combining feature because it forces Error to be Clone, which is pretty annoying for this case. It could be added again in the future if someone wants to work on it.

Bug: T319118

Edited by Legoktm

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