Doing a little cleanup/refactoring of the C++ source code

[Qqwy]

This PR makes a few small changes to improve the maintainability of the code. The individual changes are small, but because some of these patterns were repeated many times in the code, quite a few places in the code were modified.

The changes are:

• Use the compiler-checked static_cast and reinterpret_casts instead of C-style casts.
• Removed the non-standard #pragma once; standardized header guards (#ifndef ...) are enough.
• Include the C++ version of C headers (e.g. cstdbool instead of bool.h)
• Move the cleanup of AdbcError inside adbc_error_to_nif_error which allowed it to be removed everywhere this function is called.
• Ensure objects we'll use are always defined (in some cases objects were only declared before they were used, causing compiler warnings).
• Remove memset where it is not necessary now that the contents of NifRes are not separately allocated.

As added benefit, the resulting code is roughly a hundred lines shorter (without sacrificing readability) :blush: .

If you want to view one of these changes separate from the others (e.g. to better understand it): The individual commits have descriptions and each only contain a single change.

[cocoa-xu]

Hi @Qqwy thanks for the cleanup/refactoring. This looks perfect to me!