Get chunk size fix

[traktion]

• Updated the logic for calculating the chunk size when the chunk index is > 1 and the file size is less than 3 * MAX_CHUNK_SIZE (1.5 MB currently).
• The prior logic was incorrectly rounding, causing the size to be out by a small margin. This caused seek_info to return an incorrect relative_pos.
• Tested with 1 KB, 8 KB, 256 KB, 123456 bytes, 512 KB and 2048 KB over sn_httpd and confirmed all payloads were correct with Wireshark.

Link to issue: https://github.com/maidsafe/self_encryption/issues/381

Link to issue: https://github.com/maidsafe/safe_network/issues/1621

[joshuef]

nice one @traktion thank you!

can you update for the clippy errors in ci there that appears to b tripping up the other CI runs, I think 🙇

[traktion]

I'm not sure why the build is snagging on the above. It doesn't look like there should be any merge conflicts (no changes in months) and I've only added code coverage. Please lmk if there is something I need to fix! Thanks!