Fix bugs from code review, add CI and __all__

[royerloic]

Summary

• Fix end parameter double-application in aprint — e.g. aprint('hi', end='!!') produced hi!!!! instead of hi!!. Was masked for the default end='\n' because split('\n') consumed the trailing newline.
• Fix KeyboardInterrupt/SystemExit leaking _depth — changed except Exception to except BaseException in asection so Ctrl-C no longer permanently corrupts the depth counter.
• Fix silent drop of elapsed time >= 24 hours — added else clause to _print_elapsed formatting as days.
• Fix section decorator losing function metadata — added @functools.wraps.
• Fix flush parameter silently ignored in tree mode — plumbed through native_print.
• Fix set_log_max_depth docstring — said "clamped to minimum of 1" but actually clamps to 0.
• Fix Makefile publish grep prefix-matching — 2026.2.2 no longer falsely matches 2026.2.22.
• Add __all__ to __init__.py for explicit public API.
• Add CI test workflow (test.yml) — pytest across Python 3.9–3.13 + ruff lint/format check on push/PR.
• Add test gate to publish.yml — build now requires tests to pass before publishing.

Test plan

• All 42 existing tests pass
• Ruff lint: all checks passed
• Ruff format: 6 files already formatted
• Demo runs correctly end-to-end
• Edge case battery: KeyboardInterrupt, SystemExit, custom end/sep/flush, __all__, Makefile grep compatibility
• CI workflows run on this PR (test.yml)

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