refactor(kernels::grisubal): clean-up module code

[imrn99]

• rename the kernel module to routines, split its original content into file
• turn step 1.5 into step2, offset all subsequent steps
• add pre-processing routines to the routines module
• delete the grid module, move its content to model
• clean the timers implementation to hide the #[cfg(feature = "profiling")] attributes
• remove the build_mesh function to call directly step functions in the main grisubal function

I will update the doc of the algorithm in a separate PR since I intend to change more things in the doc

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 46.39640% with 238 lines in your changes missing coverage. Please review.

Project coverage is 81.89%. Comparing base (fdb2ed9) to head (3f7228c).
Report is 6 commits behind head on master.

Files with missing lines	Patch %	Lines
...mb-kernels/src/grisubal/routines/pre_processing.rs	0.00%	162 Missing ⚠️
honeycomb-kernels/src/grisubal/mod.rs	0.00%	66 Missing ⚠️
...kernels/src/grisubal/routines/compute_new_edges.rs	84.78%	7 Missing ⚠️
...ls/src/grisubal/routines/process_intersecs_data.rs	97.22%	2 Missing ⚠️
...-kernels/src/grisubal/routines/insert_new_edges.rs	98.61%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #216      +/-   ##
==========================================
+ Coverage   75.29%   81.89%   +6.59%     
==========================================
  Files          41       48       +7     
  Lines        6376     6853     +477     
==========================================
+ Hits         4801     5612     +811     
+ Misses       1575     1241     -334     

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[cedricchevalier19]

I am not convinced by putting the functions into step"I" files.

I think keeping a comment in the file and mod.rs that it is used in step "I" is more useful. And, you can name the files according to their contents.

[imrn99]

I renamed all module files to describe the step & added comments in the routines module for order.

[cedricchevalier19]

LGTM