Yellow squiggly lines begone!
Done automatically on .cpp files through `run-clang-tidy`, with manual corrections to the mistakes.
If an import is directly used, but is technically unnecessary since it's recursively imported by something else, it is *not* removed.
The tool doesn't touch .h files, so I did some of them by hand while fixing errors due to old recursive imports.
Not everything is removed, but the cleanup should be substantial enough.
Because this done on Linux, code that isn't used on it is mostly untouched.
(Hopefully no open PR is depending on these imports...)

Gets the interface out of the global namespace.

Previously this was using the default deleter (which just calls delete
on the pointer), which is incorrect, since the ENetHost instance is
allocated through ENet's C API, so we need to use its functions to
deallocate the host instead.

Public domain does not have an internationally agreed upon definition,
As such it's generally preferred to use an extremely liberal license,
which can explicitly list the rights granted by the copyright holder.
The CC0 license is the usual choice here.

This "relicensing" is done without hunting down copyright holders, since
it is presumed that their release of this work into the public domain
authorizes us to redistribute this code under any other license of our
choosing.

Same behavior, but allows the use of non-allocating string types with
the interface.

Prevents implicit conversions and prevents identifiers from polluting
the class scope.