Improve error message for message length mismatch

[rohitpaulk]

Instead of just saying "Length mismatch", let's say:

Expected 28 bytes, received 24 bytes
Expected: ....
Received: ... 

We might also be able to re-use https://github.com/codecrafters-io/tester-utils/blob/master/bytes_diff_visualizer/bytes_diff_visualizer.go in some way, but probably not needed here since there's no non-ascii characters involved

[linear[bot]]

CC-1040 Improve error message for message length mismatch

[rohitpaulk]

Thanks to @b14cknc0d3 for reporting this!

[ryan-gang]

Should be fixed.