Move to new t8code version 3.0.0

[benegee]

• Move to latest t8code version
• Use t8code's cmake support
• Enable new t8code Fortran interface
• Add t8code Fortran controller example
• Adapt the docs

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.75%. Comparing base (dd3cce5) to head (2ae6191).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #215      +/-   ##
==========================================
+ Coverage   80.52%   81.75%   +1.23%     
==========================================
  Files          19       21       +2     
  Lines         724      773      +49     
  Branches       50       52       +2     
==========================================
+ Hits          583      632      +49     
  Misses        137      137              
  Partials        4        4              

Flag	Coverage Δ
unittests	81.75% <100.00%> (+1.23%)	⬆️

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[benegee]

It's been a while, but we have something to review @sloede !

Note that PackageCompiler build currently fails but will be fixed in course of #207 hereafter.

[benegee]

Another ping @sloede as requested. 😃

[sloede]

Generally LGTM, just a few questions. Also, some tests seem to be failing?

[benegee]

Generally LGTM, just a few questions. Also, some tests seem to be failing?

This is package compiler and will hopefully be fixed in course of #207 hereafter.

[sloede]

Thanks!