Function patch 

pub fn patch<T, W>(old: &[u8], patch: &mut T, new: &mut W) -> Result<()>
where
    T: Read,
    W: Write + DerefMut<Target = [u8]>,

Apply a patch to an “old” file, returning the “new” file.

old is the old file, patch will be read from with the patch, new is the buffer that will be written into.

This is optimized for performance with:

• Bulk read operations
• SIMD-friendly memory access patterns
• Proper validation with early errors