Iterator peek next

[cgestes]

Please review. Some changes may be better done in another way.

This PR is needed to support Markdown auto formatting rules in Notus.

[cgestes]

I can move the extension in Notus. No issue. I believe they should just exist somewhere cause they are a pain in the ass to write.

I did implement peek before but it makes the code that uses it hard to grok.

And peek now is:

Final newIter = iter.clone()
newIter.next()

Also I believe skipToBeginningOfLineBeforeIndex would be more optimised if we skip to index and then look backward. Otherwise we look for \n on every single line from start of doc.

[cgestes]

For EOF I like the idea too. Will implement in a future PR. I came to it cause the doc on DeltaItarator.next was incorrect, so I reimplement by mistake what the doc was saying...then had to fix the test in Notus and noticed it was all making more sense 😅

[codecov[bot]]

Codecov Report

Merging #26 (b8c13d5) into master (4846633) will decrease coverage by 10.48%. The diff coverage is 43.75%.

:exclamation: Current head b8c13d5 differs from pull request most recent head c950b1b. Consider uploading reports for the commit c950b1b to get more accurate results

@@             Coverage Diff             @@
##           master      #26       +/-   ##
===========================================
- Coverage   93.56%   83.08%   -10.49%     
===========================================
  Files           1        1               
  Lines         342      396       +54     
===========================================
+ Hits          320      329        +9     
- Misses         22       67       +45     

Impacted Files	Coverage Δ
lib/quill_delta.dart	83.08% <43.75%> (-10.49%)	:arrow_down:

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