Changing behaviour for allocate_vector

[JordiManyer]

Up to now, allocate_vector used the zeros method to create the vector. This not only allocates, but also initializes. Now this is no longer the case.

I have gone through the functions using allocate_vector, allocate_in_domain and allocate_in_range and did the necessary updates.
Notably, the functions zero_free_values and zero_dirichlet_values were not explicitly filling the newly allocated vector with zeros, but were relying on the function to set the values to zero. This is now explicit.

Also, now that the API for allocate_vector is more robust, I've gotten rid of some specializations for zero_free_values that are now redundant.

[codecov-commenter]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (68db8cb) 88.08% compared to head (5438ce0) 88.10%.

Files	Patch %	Lines
src/ODEs/TransientFETools/TransientFESpaces.jl	0.00%	3 Missing ⚠️
src/Algebra/AlgebraInterfaces.jl	50.00%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #963      +/-   ##
==========================================
+ Coverage   88.08%   88.10%   +0.02%     
==========================================
  Files         177      177              
  Lines       21077    21075       -2     
==========================================
+ Hits        18566    18569       +3     
+ Misses       2511     2506       -5     

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