Fixes #2615

Closes #2603

* Add new SKIP macro for skipping tests at runtime

This adds a new `SKIP` macro for dynamically skipping tests at runtime.
The "skipped" status of a test case is treated as a first-class citizen,
like "succeeded" or "failed", and is reported with a new color on the
console.

* Don't show "skipped assertions" in console/compact reporters

Also extend skip tests to cover a few more use cases.

* Return exit code 4 if all test cases are skipped

* Use LightGrey for the skip colour

This isn't great, but is better than the deep blue that was borderline
invisible on dark backgrounds. The fix is to redo the colouring
a bit, including introducing light-blue that is actually visible.

* Add support for explicit skips in all reporters

* --allow-running-no-tests also allows all tests to be skipped

* Add docs for SKIP macro, deprecate IEventListener::skipTest

Co-authored-by: Martin Hořeňovský <martin.horenovsky@gmail.com>

GCC 13 (as usual for new compiler releases) shuffles around some
internal includes and so <cstdint> is no longer transitively included.

Explicitly include <cstdint> for uint64_t.

```
FAILED: src/CMakeFiles/Catch2.dir/catch2/internal/catch_clara.cpp.o
/usr/lib/ccache/bin/g++-13  -I/var/tmp/portage/dev-cpp/catch-3.0.1/work/Catch2-3.0.1/src/catch2/.. -I/var/tmp/portage/dev-cpp/catch-3.0.1/work/Catch2-3.0.1_build/generated-includes  -O2 -pipe
-march=native -fdiagnostics-color=always -frecord-gcc-switches -Wreturn-type -D_GLIBCXX_ASSERTIONS  -ggdb3 -fdiagnostics-color=always
-ffile-prefix-map=/var/tmp/portage/dev-cpp/catch-3.0.1/work/Catch2-3.0.1=. -Wall -Wc++20-compat -Wcast-align -Wcatch-value -Wdeprecated -Wexceptions -Wextra -Wextra-semi -Wfloat-equal -Winit-self
-Wmisleading-indentation -Wmismatched-new-delete -Wmismatched-tags -Wmissing-braces -Wmissing-declarations -Wmissing-noreturn -Wnull-dereference -Wold-style-cast -Woverloaded-virtual -Wparentheses
-Wpedantic -Wreorder -Wshadow -Wstrict-aliasing -Wsuggest-override -Wundef -Wuninitialized -Wunreachable-code -Wunused -Wunused-function -Wunused-parameter -Wvla -MD -MT
src/CMakeFiles/Catch2.dir/catch2/internal/catch_clara.cpp.o -MF src/CMakeFiles/Catch2.dir/catch2/internal/catch_clara.cpp.o.d -o src/CMakeFiles/Catch2.dir/catch2/internal/catch_clara.cpp.o -c
/var/tmp/portage/dev-cpp/catch-3.0.1/work/Catch2-3.0.1/src/catch2/internal/catch_clara.cpp
In file included from /var/tmp/portage/dev-cpp/catch-3.0.1/work/Catch2-3.0.1/src/catch2/internal/catch_clara.cpp:12:
/var/tmp/portage/dev-cpp/catch-3.0.1/work/Catch2-3.0.1/src/catch2/../catch2/internal/catch_string_manip.hpp:47:14: error: 'uint64_t' in namespace 'std' does not name a type; did you mean 'wint_t'?
   47 |         std::uint64_t m_count;
      |              ^~~~~~~~
      |              wint_t
/var/tmp/portage/dev-cpp/catch-3.0.1/work/Catch2-3.0.1/src/catch2/../catch2/internal/catch_string_manip.hpp:51:42: error: expected ')' before 'count'
   51 |         constexpr pluralise(std::uint64_t count, StringRef label):
      |                            ~             ^~~~~~
      |                                          )
```

This is needed so that we can use conjunction and other logical
type traits to workaround issue with older GCC versions (8 and
below), when they run into types that have ambiguous constructor
from `0`, see e.g. #2571.

However, using conjunction and friends in the SFINAE constraint
in the template parameter breaks for C++20 and up, due to the new
comparison operator rewriting rules. With C++20, when the compiler
see `a == b`, it also tries `b == a` and collects overload set
for both of these expressions.

In Catch2, this means that e.g. `REQUIRE( 1 == 2 )` would lead
the compiler to check overloads for both `ExprLhs<int> == int`
and `int == ExprLhs<int>`. Since the overload set and SFINAE
constraints assume that `ExprLhs<T>` is always on the left side,
when the compiler tries to resolve the template parameters, all
hell breaks loose and the compilation fails.

By moving the SFINAE constraints to the return type, the compiler
can discard the switched expression without having to resolve
the complex SFINAE constraints, and thus everything works the
way it is supposed to.

Fixes #2571