Fix Windows CI test run: 0xc0000135 (missing libpng16-16.dll on PATH) (issue 7)

[QuasarAppCI]

Fixes the failing windows-latest (Release) leg of the CI pipeline delivered in
PR #10. After the merge, workflow_dispatch run 38415068822 on main
(2026-10-13T14:38Z) failed in Run Tests; the Linux leg passed. Related: #7.

Root cause (two independent Windows issues)

1. STATUS_DLL_NOT_FOUND (0xc0000135) — OpenSimplex2tests.exe (built with
the aqt MinGW) links against the MSYS2 mingw-w64-x86_64-libpng and at runtime
needs libpng16-16.dll (+ libz-1.dll) from <msys2>/mingw64/bin. But
msys2/setup-msys2@v2 adds only the MSYS2 root to the Windows PATH (verified
against the action source, SHA ec48f7c), so the DLL search path never reaches
mingw64/bin. The test target's deploy step (cqtdeployer clear) copies the
MinGW runtime but cannot find libpng16-16.dll (the same "Cannot find the
library for dependency libpng16.so.16" notice is printed on the Linux leg, where
the OS loader finds the system libpng — which is why Linux passed).

2. Stack overflow (0xc000013d, exposed by fix 1) — once the DLLs resolved,
the test executable crashed with Stack overflow: main() in
tests/test_OpenSimplex2F.c allocates three 512x512xuint32_t buffers (3 x 1MB)
on the stack. The default Windows thread stack is 1MB; Linux only survives
because its default stack is 8MB.

Fix

1. One Windows-only workflow step appends <msys2-location>/mingw64/bin to
   GITHUB_PATH right after the MSYS2 setup step, so the test executable can
   resolve the MSYS2 DLLs at runtime (.github/workflows/ci.yml, +9 lines).
2. The three image buffers in main() are moved to static storage (static
   -> BSS), removing the 3MB stack usage on all platforms
   (tests/test_OpenSimplex2F.c, +8/-3 lines). Test output is unchanged.

Verification

• YAML validated; total diff: 2 files, +17/-3.
• Linux leg re-verified locally: configure + build + cmake --build build --target test exit 0; test2d/test3d/test4d.png regenerated with identical
  sizes (103274/211556/185219 bytes).
• PR CI (pull_request) runs on every push — the first run (38417362685)
  confirmed fix 1 (error moved 0xc0000135 -> 0xc000013d); the run triggered by
  this commit verifies fix 2 end-to-end.

Review round (2026-10-13): readable test output

EndrII: "good - but tests still nothing to print - please add readable output
of tests."

• The test executable now prints a per-test report for the CI log: noise
  function name, min/max/mean of the generated values, the generated PNG with
  its byte size and PASS/FAIL per image, plus a final "Result: N/3 tests
  passed" summary. On failure it prints the reason and returns a non-zero
  exit code so the test target fails loudly. Each image is validated
  against the documented [-1, 1] noise range and that its PNG was actually
  written (commit 1ae96ec).
• CI run 38422350598 (head 1ae96ec): SUCCESS — ubuntu-latest (Release) and
  windows-latest (Release) both green; the readable report is visible in
  the Run Tests log of both legs (noise min/max/mean identical on Linux
  and Windows).

[EndrII]

good - but tests still nothing to pring - please add readable output of tests.

[QuasarAppCI]

Done (commit 1ae96ec). The test executable now prints a readable report for the CI log: a per-test line with noise value min/max/mean, the generated PNG size and PASS/FAIL (with a reason on failure), plus a final 'Result: N/3 tests passed' summary; the test target returns a non-zero exit code when any check fails. Each image is checked for the documented [-1, 1] value range and that its PNG was actually written. Generated PNGs are byte-identical in size to before (103274/211556/185219 bytes). CI on this push verifies both legs.

[QuasarAppCI]

Merged into main as b4be1e9 — thanks for the review! Verified the merged head locally (configure + build + test target): 3/3 tests pass, readable per-test report in the log.