improved diff report

[gkampitakis]

Some views:

How a diff currently looks

How a diff looks with this pr

How a diff looks with vs code diff

Experimenting with better diff.

• [x] More readable color
• [x] Numbers and signs for diff ( so we can understand the diff even if no color supported )
• [x] Skip from printing the whole snapshot even if there are no diffs for many lines
• [x] Better diffing when insertions and deletions happen on the same line ( not sure if can be done easily )
• [x] Unit Testing
• [x] Clean code
• [x] Update colors on summary messages