Improve RF simulation docs formatting slightly

[nikosavola]

This PR improves formatting in RF simulation docs slightly:

• add a hide-input tag to the imports in Palace scattering example
• add a hide-output tag to Palace simulations (though not yet run in CI, Run Palace tests in CI #64)
• remove empty lines before code to run

[codecov]

Codecov Report

Merging #115 (244fedb) into main (a5c55c6) will not change coverage.
Report is 20 commits behind head on main.
The diff coverage is 34.69%.

@@           Coverage Diff           @@
##             main     #115   +/-   ##
=======================================
  Coverage   40.14%   40.14%           
=======================================
  Files         170      170           
  Lines       10529    10529           
=======================================
  Hits         4227     4227           
  Misses       6302     6302           

Files Changed	Coverage Δ
...umerical/write_sparameters_lumerical_components.py	35.00% <0.00%> (ø)
gplugins/tidy3d/get_simulation.py	71.34% <ø> (ø)
gplugins/femwell/solve_thermal.py	17.64% <11.11%> (ø)
gplugins/web/main.py	36.47% <16.66%> (ø)
gplugins/femwell/__init__.py	100.00% <100.00%> (ø)
gplugins/gmsh/__init__.py	100.00% <100.00%> (ø)
gplugins/gmsh/uz_xsection_mesh.py	63.39% <100.00%> (ø)
gplugins/gmsh/xy_xsection_mesh.py	55.76% <100.00%> (ø)
gplugins/gmsh/xyz_mesh.py	82.35% <100.00%> (ø)
...ugins/path_length_analysis/path_length_analysis.py	58.05% <100.00%> (ø)
... and 1 more

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