fix: improve snapshot diff with newlines

[gkampitakis]

When creating a snapshot it's saved the format involves adding a newline

[ Test Name ]
\n <- newline
snapshot body
\n  <- newline
---

Until now when creating a diff snashot this new line was added as part of the diff calculation. This did not create false diff reports but when a new a diff report is created those new lines are reported as part of the snapshot body that can create confusion.

Examples before and after:

and also some better improvements on single line diffs