[cmake] Conda build with upstream tfel/mgis packages

See merge request ogs/ogs!5216

This reverts commit ea93ab7a.

[Tests] better code quality in TH2M py notebooks

See merge request ogs/ogs!5217

replaced vtuIO with ogstools
added assertions
reduced repetitions

[guix] Re-introduce pinning of guix channels.

See merge request ogs/ogs!5219

Fix link to msh2vtu

See merge request ogs/ogs!5218

Can build with OGS_USE_MFRONT=ON in a conda env. E.g.:

environment.yml:

name: ogs-conda-dev
channels:
- conda-forge
dependencies:
- eigen
- exprtk
- hdf5
- libboost-python-devel
- libxml2
- metis
- nlohmann_json
- pybind11
- python
- range-v3
- tclap
- vtk >=9.3.0
- zlib
- mfront 4.2
- mgis 2.2

conda env create -f environment.yml
conda activate ogs-conda-dev
cmake --preset release -DOGS_USE_MFRONT=ON

Changes to the end time of the HT_a_DECOVALEX_THMC_based_Example ctest
were incorrect.

weighting factor used in HEAT_TRANSPORT_BHE process

See merge request ogs/ogs!5179

change the weighting factor to use abs val

weighting factor consider both M and K matrix

fix clang-format error

Refactor SpatialPosition for more efficient memory usage

See merge request ogs/ogs!5212

Reduce some more redundancy in LiquidFlow and Hydromechanics

See merge request ogs/ogs!5208

getFluidDensity and getFluidDensityAndViscosity for
single phase flow models.

Improves constness of the local SpatialPosition variables.

Saves 16 bytes; one bitset (8) vs three optionals (24).
Remove only internally used clear() function from I/F.

Effectively not used anyway.

And remove the corresponding functions in SpatialPosition.

[PL/SDN] Move divergence computation

See merge request ogs/ogs!5213

The computation is used only once and had a missing
header include (Eigen/Core). Replaced with more efficient
code directly in FEM.

Update guix to use upstream tfel / mgis / exprtk.

See merge request ogs/ogs!5211