Tracker for issues in code comments

[pentschev]

Various issues are currently commented in code, this aims to track those:

C++

• Ensure it's safe to require GIL in ucxx::python::Future::~Future()
• Move away from std::shared_ptr<void>
• Handle errors in ucxx::RequestTagMulti::markCompleted()
• Prevent throwing exceptions in ucxx::RequestTagMulti callbacks
• Fix destruction of ucxx::RequestTagMulti's BufferRequest
• Ensure progress thread progresses before checking ucxx::Worker::tagProbe()

C++ Tests

• Use a timeout when probing for tags

Python

• Deprecate and remove old exception names
• Replace unique_ptr by stack object
• Use cdef enum class after moving to Cython 3.x, similarly here

Python tests and benchmarks

• Add back custom UCXCanceledError message, if it's worth the effort
• Remove "Message truncated" match when Python futures accept custom exception messages
• Fix broken wireup message
• Find root cause for hang in Queue.get() and fix

CMake

• Do not require C module to build Python extensions
• Remove find NumPy workaround

Build scripts

• Fix defaults for variables that are not externally defined (maybe raise fatal error?), taken from cudf