This formats all copyright comments according to SPDX formatting guidelines.
Additionally, this resolves the remaining GPLv2 only licensed files by relicensing them to GPLv2.0-or-later.

Now that we have most of core free of shadowing, we can enable the
warning as an error to catch anything that may be remaining and also
eliminate this class of logic bug entirely.

Makes our error coverage a little more consistent across the board by
applying it to Linux side of things as well. This also makes it more
consistent with the warning settings in other libraries in the project.

This also updates httplib to 0.7.9, as there are several warning
cleanups made that allow us to enable several warnings as errors.

Same behavior, minus unnecessary inclusions where not necessary.

enum class elements from the same enum can already be compared against
one another without the need for explicitly defined comparison
operators.

Several classes have a lot of non-trivial members within them, or don't
but likely should have the destructor defaulted in the cpp file for
future-proofing/being more friendly to forward declarations.

Leaving the destructor unspecified allows the compiler to inline the
destruction code all over the place, which is generally undesirable from
a code bloat perspective.

Cuts down on include dependencies, resulting in less files that need to
be rebuilt when certain things are changed.