Improve exception handling for bad any cast

[ankane]

Hi, currently bad any cast causes the Ruby program to crash, which isn't ideal for end users.

libc++abi: terminating due to uncaught exception of type std::bad_any_cast: bad any cast
SignalException: SIGABRT (SignalException)

This PR changes it to raise an exception (with some context) instead.

RuntimeError: Bad any cast for DataSketches::HllUnion update

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I'm seeing this error across a number of projects, but still trying to figure out the cause. From the error, it seems like NativeRegistry may be getting corrupted, or the function is never properly registered to begin with (as it either happens never or every time for the lifetime of the program).

[ankane]

It looks like the bad any cast errors are due to hash collisions in natives_, which aren't currently handled.

DataSketches::HllUnion update 256351383834
DataSketches::KllFloatsSketch max_value 256351383834

Edit: Looks like the issue was introduced in 819515b

[ankane]

Closing in favor of #208