Block size

Add an option to retrieve the block size for a file and return an error if the filesystem type is not supported

The issue does not name files, tests, or an entry point. Start by locating the command-line option handling and the code that opens or writes the target file, then inspect how filesystem information is currently obtained. Done means exposing a block-size option and returning an error for unsupported filesystem types, with the relevant behavior covered by tests if the repository has them.

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