--coverage=DIR runs every attempt in a process of its own and keeps the
coverage of each test, for binaries built with LLVM source-based
coverage (Clang: -fprofile-instr-generate -fcoverage-mapping) or gcov
(GCC: --coverage).

How it works:

- The scheduler gives each attempt a fresh worker, as --isolate does,
  and sets LLVM_PROFILE_FILE and GCOV_PREFIX for it: the profile the
  process writes at exit is then the coverage of that one test, in
  DIR/profiles/t<index>-a<attempt>.profraw or a .gcov directory. Each
  runtime reads its own variable, so no symbol of either runtime is
  looked up: weak references would not pull them out of their static
  archives, and Mach-O does not allow undefined weak symbols.
- A process that runs other tests first (bisection) writes beside the
  profiles, never into one. The attempt records its profile, also in
  the JSON results.
- The profiles of an earlier run are removed when the run starts,
  because gcov adds to the .gcda files it finds.
- After the run, CoverageReport reads the last profile of every test:
  llvm-profdata and llvm-cov (PATH, xcrun on macOS, or
  CATCH3_LLVM_PROFDATA / CATCH3_LLVM_COV) export LCOV, gcov (or
  CATCH3_GCOV) writes JSON next to a copy of the .gcno. The result is
  DIR/coverage.json, the files, lines and branches each test reached,
  and DIR/coverage.lcov for the whole run. Without the tools the
  profiles stay and the run says so.
- --coverage with --in-process or --break is refused.

Tests: option parsing, LCOV reading and writing, gcov JSON, and an
integration test on CoverageFixture, a binary CMake builds with the
coverage flags of Clang or GCC: two tests reach different lines, each
map holds only its own, the LCOV report holds both, and a stale profile
of an earlier run is gone. Locally all 84 CTest tests pass with Clang,
and the coverage tests pass with GCC (built with
CATCH3_ENABLE_WERROR=OFF: Catch3 does not build with GCC's warnings as
errors, before and after this change).

CI: the Linux jobs install LLVM's coverage tools, a new job checks the
gcov path with GCC, and CATCH3_COVERAGE_REQUIRE_MAP turns a missing map
into a failure on Linux and macOS instead of a skip. MSVC has no
source-based coverage, so its builds skip those tests; the roadmap
lists step 4 as in progress until Windows with clang-cl is tested.

Pin the CodeQL action to its v4.38.2 release

The init and analyze steps were pinned to 7999b86c, a commit no release tag
points at, with a "# v4" comment that names another commit (zizmor
ref-version-mismatch, two code-scanning alerts). Both steps now use
2892aa5e, the commit of v4.38.2, with that exact version as the comment.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Withhold secret-looking variables from the processes the runner starts

EnvironmentBlock replaced every non-ASCII character of an inherited name
with '?' before asking whether to withhold it, so --pass-env=MY_?_TOKEN
kept an unrelated MY_é_TOKEN. Names are now converted with Narrow, as
everything else the runner compares.

A block whose variables were all withheld, with no additions, ended in one
terminator; CreateProcessW needs two for an empty block.

The amalgamated sources are regenerated for the runner changes.

Workers and the other processes the runner starts copied its whole
environment, tokens and passwords included. ChildProcess::Start now
leaves out every variable whose name contains, in any case, TOKEN,
SECRET, PASSWORD, PASSWD, CREDENTIAL, API_KEY, APIKEY, PRIVATE_KEY or
ACCESS_KEY (IsSecretVariable), unless ChildOptions::keptEnvironment
names it; names compare without case on Windows.

--pass-env=NAME, repeatable, and "pass-env" in catch3.json keep a
variable for the tests. The runner itself still starts with the whole
environment, so code that runs before the first worker sees it;
docs/progmasoft-runner.md says so.

A runner test starts the shell's environment listing with a secret and
a plain variable set, sees only the plain one, and sees the secret once
it is kept.

Move the tools from Python to C++17 and Bazel

Release Catch3 0.3.0.2