Time space dependent trap density

[RemDelaporteMathurin]

Proposed changes

Implemented a time and space dependent trap density #644

Types of changes

What types of changes does your code introduce to FESTIM?

• [ ] Bugfix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Code refactoring
• [ ] Documentation Update (if none of the other choices apply)
• [ ] New tests

Checklist

• [ ] Black formatted
• [ ] Unit tests pass locally with my changes
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have added necessary documentation (if appropriate)

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 47.61905% with 22 lines in your changes missing coverage. Please review.

Project coverage is 97.05%. Comparing base (3fc02da) to head (bc4636b).

Files	Patch %	Lines
festim/species.py	36.36%	21 Missing :warning:
festim/hydrogen_transport_problem.py	88.88%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## fenicsx #782 +/- ## =========================================== - Coverage 98.39% 97.05% -1.34% =========================================== Files 28 28 Lines 1554 1594 +40 =========================================== + Hits 1529 1547 +18 - Misses 25 47 +22 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.