Summary of Changes

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This pull request significantly enhances mruby's C-level error handling by introducing a robust 'ensure'-like macro. This change streamlines resource management and exception safety in C extensions and core components, making the codebase more resilient and easier to maintain by centralizing cleanup logic. It also simplifies gem dependencies where error handling was previously managed.

Highlights

New MRB_ENSURE() Macro: Introduced a new C macro, MRB_ENSURE(), which provides 'ensure'-like functionality for C code within mruby, guaranteeing that a cleanup block is executed even if a global jump (exception) occurs during the protected code execution.
Refactoring Existing Error Handling: Existing usages of mrb_protect_error() and mrb_ensure() across mruby-array-ext, mruby-bigint, and mruby-eval gems have been refactored to utilize the new MRB_ENSURE() macro, simplifying the error handling and cleanup patterns.
Dependency Removal: The mruby-array-ext gem's explicit dependency on mruby-error has been removed, as the core error handling mechanisms are now integrated directly into mruby.h and mruby/error.h via the new macro.
Unique Name Generation: Added helper macros (MRB_UNIQNAME, MRB_UNIQNAME_1, MRB_UNIQNAME_2) to include/mruby.h to generate unique variable names, which are used internally by MRB_ENSURE() to prevent naming conflicts.

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