If clipboard operations throw an exception, don't crash

[waf]

If clipboard operations throw an exception, don't crash. However, if the exception is because the user is on Linux and xsel is not installed, then the clipboard operations will never work, so we should throw an exception telling the user to install xsel.

[codecov]

Codecov Report

❌ Patch coverage is 96.42857% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.2%. Comparing base (f59d789) to head (e410516).

Files with missing lines	Patch %	Lines
src/PrettyPrompt/Panes/CodePane.cs	95.2%	1 Missing ⚠️
src/PrettyPrompt/Prompt.cs	0.0%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #300     +/-   ##
=======================================
+ Coverage   85.8%   86.2%   +0.4%     
=======================================
  Files         47      47             
  Lines       4030    4063     +33     
  Branches     676     677      +1     
=======================================
+ Hits        3460    3505     +45     
+ Misses       404     392     -12     
  Partials     166     166             

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