Creates dedicated module to VolumeModel to separate it from core definitions

[GabrielJMS]

• Please check if the PR fulfills these requirements

• [x] The commit messages follows our guidelines (explicit, in english)

• [x] Tests for the changes have been added (for bug fixes / features)

• [ ] Docs have been added / updated (for bug fixes / features)

• [x] CHANGELOG.md has been updated

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

• [ ] Bug fix:

• [ ] New features:

• [ ] Documentation

• [x] Optimization

• Other information:

  closes:

  https://github.com/Dessia-tech/volmdlr/issues/1327