This change removes the existing undefined behavior from `LogicError`, so we can be certain that there will be always a stacktrace.
De-referencing a null pointer is an old trick to generate `SIGSEGV`, which would typically also create a stacktrace. However it is also an undefined behaviour and compilers can do something else. A more robust way to create a stacktrace while crashing the program is to use `std::abort`, which we have also used in this location for a long time. If we combine the two, we might not get the expected behaviour - namely, the nullpointer deref followed by `std::abort`, as handled in certain compiler versions may not immediately cause a crash. We have observed stacktrace being wiped instead, and thread put in indeterminate state, then stacktrace created without any useful information.
The codebase is filled with includes that are unused, and which thus can be removed. At the same time, the files often do not include all headers that contain the definitions used in those files. This change uses clang-format and clang-tidy to clean up the includes, with minor manual intervention to ensure the code compiles on all platforms.
* Copy Antithesis SDK version 0.4.0 to directory external/
* Add build option `voidstar` to enable instrumentation with Antithesis SDK
* Define instrumentation macros ASSERT and UNREACHABLE in terms of regular C assert
* Replace asserts with named ASSERT or UNREACHABLE
* Add UNREACHABLE to LogicError
* Document instrumentation macros in CONTRIBUTING.md
