Add py.typed marker for PEP 561 compliance

[KRRT7]

Adds the empty py.typed marker file to src/danom/ per PEP 561.

Without this, mypy (and other type checkers) treat danom as an untyped package — every @safe decorated function loses its type signature, and from danom import safe triggers import-untyped errors under strict = true.

With the marker, mypy uses danom's inline annotations directly. No code changes needed — just the marker file.

[codspeed-hq]

Merging this PR will not alter performance

✅ 21 untouched benchmarks

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_{Comparing KRRT7:feat/add-py-typed (2525ecf) with dev (c7e2b72)}