Ensure reformat-on-submit is handled correctly

[waf]

If the caller uses the autoformat callback at the same time as they're submitting the prompt, the autoformatted text is not rendered on screen and the returned text is also not autoformatted. This PR fixes both.

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.4%. Comparing base (50fab93) to head (096f95f).

Files with missing lines	Patch %	Lines
src/PrettyPrompt/Panes/CodePane.cs	50.0%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #301     +/-   ##
=======================================
+ Coverage   86.3%   86.4%   +0.1%     
=======================================
  Files         47      47             
  Lines       4073    4081      +8     
  Branches     678     679      +1     
=======================================
+ Hits        3516    3530     +14     
+ Misses       392     384      -8     
- Partials     165     167      +2     

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