Allow the Wave case runner to show help before locating a compiler

[LunaStev]

tools/run_tests.py calls resolve_wavec() at module scope before parsing arguments. In a checkout without a built compiler, python tools/run_tests.py --help exits with a build-first error instead of showing usage. It also creates a temporary output directory before argparse handles help, leaving an unnecessary directory on this path.

Source evidence at the head of #520:

• tools/run_tests.py:92 — WAVEC = resolve_wavec()
• tools/run_tests.py:99 — TEST_OUTPUT_DIR = Path(tempfile.mkdtemp
• tools/run_tests.py:150 — ARGS = parse_args()

Acceptance:

• Parse CLI arguments and handle help/usage errors before compiler discovery or output-directory creation.
• Make normal execution retain the existing actionable missing-compiler error.
• Add lightweight Python tests with a temporary checkout or mocked discovery; no compiler build or network access should be needed.
• Ensure the help path creates no output directories.

Related: #499 covers finding MSVC compiler binaries; this issue concerns CLI startup order.

Audit status: identified by static source inspection; the scenarios above have not been executed during this audit. The permalink fixes the reviewed revision; this report does not claim the defect was introduced by #520.

[IbrahimCodes347]

I've prepared a fix for this and am opening a draft PR for review shortly. If you're already working on it, let me know and I'll back off / close mine.