Decode binary file contents before detecting frontmatter

[vitalivo]

This replaces #138, which was accidentally closed and its source fork deleted. The implementation is unchanged; the original discussion and reviews remain linked there.

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load(BytesIO(...)) and load() on a file opened in binary mode raise TypeError: cannot use a string pattern on a bytes-like object. Format detection runs on the raw bytes before loads() can decode them.

Delegate format detection to loads(), which already decodes with the supplied encoding and respects an explicit handler. Tests cover UTF-8 and UTF-16 byte streams, a binary JSON-frontmatter file, metadata defaults, and a text-stream control.

Validation: the three binary cases fail before the fix; all 69 tests and doctests pass afterward, and mypy . passes.