Function default_seek 

pub fn default_seek<F>(
    current_offset: off_t,
    target: SeekTarget,
    compute_end: F,
) -> Result<off_t, Errno>
where
    F: FnOnce() -> Result<off_t, Errno>,

Implement the seek method for a file. The computation from the end of the file must be provided through a callback.

Errors if the calculated offset is invalid.

• current_offset: The current position
• target: The location to seek to.
• compute_end: Compute the new offset from the end. Return an error if the operation is not supported.