Catch3 keeps Catch2's API for writing tests (test cases, sections,
assertions, matchers, generators, listeners, benchmarks) and replaces its
session, command line and reporters with a runner of its own.

The runner starts the test binary again as worker processes that take the
next test when they are free. A crash, an exit or a hang ends one test, not
the run. On top of that it adds:

- retries that tell deterministic, flaky and order-dependent failures
  apart, and a bisection that names the test leaving state behind;
- a history of verdicts and durations, kept under a file lock, that drives
  automatic quarantine, adaptive time limits, predictive ordering,
  incremental runs, failure replay and analytics;
- selection by change, past failure or prediction, dependency closure,
  and sharding by a stable hash or by recorded durations;
- tags for serial and isolated tests, shared resources, dependencies,
  time limits and retries;
- a failure category, a signature, an analysis and a replay command for
  every failure;
- console, JUnit XML (with flakyFailure and rerunFailure), JSON and Chrome
  trace reports, and a versioned discovery listing (--list=json);
- a temporary directory per test (TMPDIR, TMP, TEMP and
  TestTemporaryDirectory());
- Bazel's test environment: XML output file, test filter, sharding, seed,
  premature exit file and undeclared outputs.

The command line is parsed by a hand-written, typed parser. Catch::Session
remains as a thin facade over the runner for custom main functions.

The result model in Progmasoft/Catch3/Results.hpp was rewritten around
tests and attempts, and the JUnit writer now writes it. The property
engine's example database is updated under a file lock with an atomic
rename, so parallel workers can write it at the same time.

Removed: Clara, the command-line and reporter-spec parsers, every reporter
and CATCH_REGISTER_REPORTER, listing, text flow, console colour and width,
the JSON and XML writers, sharding in the test registry, approval tests and
their baselines, Conan packaging, and the unused third_party/clara.hpp.
Listeners keep working; reporters' list and skip events are gone.

The Catch2 library is now compiled as C++20; code that includes only
Catch2's headers still needs C++14. Duplicate test cases are still refused
at start-up. Version 0.3.0.

ExtraTests now turn exceptions off for clang-cl with MSVC-style options,
which -fno-exceptions did not do.

As with the JSON writer, the old code was made to be simple and
for each char just decided whether it needs escaping, or should be
written as-is. The new code instead looks for characters that need
escaping and batches writes of characters that do not.

This provides 4-8x speedup (length dependent) for writing strings
that do not need escaping, and keeps roughly the same performance
for those that do need escaping.

Most of these will not matter in practice due to C++14 imposing
significant limitations on what else we can make constexpr, and we cannot
have references outliving the constexpr context either way.

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):
      |                            ~             ^~~~~~
      |                                          )
```

The license file was renamed with 6a502cc2f5fedd59b3495b58708f0d6d987ed9e1

There is no good reason to provide a "add empty line" primitive
for writing XML documents, and the fact that it remains unused
after all the time it was provided only confirms this further.

Previously, string literals and `std::string`s would match the
template variant, which would serialize them into a stream and then
call the `StringRef` overload for resulting string. This caused
bunch of codebloat and unnecessary pessimization for common usage.