Add possibility to draw last step to IP

[trappitsch]

Without ever typing in the IP, this will draw the last step to the defined IP with a hollow arrow. In the scheme, it will indicate that the last step is actually a lower limit / upper limit for the wavelength.

[codecov]

Codecov Report

Attention: Patch coverage is 94.87179% with 2 lines in your changes missing coverage. Please review.

Project coverage is 94.05%. Comparing base (0018272) to head (8b6ba3d).
Report is 15 commits behind head on main.

Files	Patch %	Lines
src/rimsschemedrawer/plotter.py	81.81%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #24      +/-   ##
==========================================
+ Coverage   94.03%   94.05%   +0.01%     
==========================================
  Files           9        9              
  Lines         671      706      +35     
==========================================
+ Hits          631      664      +33     
- Misses         40       42       +2     

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