Steady state callback

[LasNikas]

I tested the callback with the pipe_flow_2d.jl example. It terminates after ~0.8sec. I consider the change in kinetic energy in a 0.002*10 interval.

pp_callback = PostprocessCallback(; dt=0.02, kinetic_energy)

steady_state = SteadyStateCallback(; dt=0.002, interval_size=10, abstol=1.0e-8, reltol=1.0e-6)

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 52.94118% with 32 lines in your changes missing coverage. Please review.

Project coverage is 68.47%. Comparing base (c744cad) to head (3618976). Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/callbacks/steady_state_reached.jl	45.76%	32 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #601      +/-   ##
==========================================
- Coverage   68.71%   68.47%   -0.25%     
==========================================
  Files          86       87       +1     
  Lines        5299     5360      +61     
==========================================
+ Hits         3641     3670      +29     
- Misses       1658     1690      +32     

Flag	Coverage Δ
unit	68.47% <52.94%> (-0.25%)	:arrow_down:

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