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Implement `ExtractV1File` where the function takes path to a CARv2 file
and efficiently extracts its inner CARv1 payload. Note, the
implementation only supports CARv2 as input and returns a dedicated
error if the supplied input is already in CARv1 format.

Implement benchmarks comparing extraction using `Reader` vs
`ExtractV1File`.

Implement tests that assert in-place extraction as well as invalid input
and both v1/v2 input

Fixes #207