Add unit tests for `replica_exchange_EE.py`, the `utils` module and a part of the `analysis` module

[wehs7661]

In this PR, we aim to enhance the code coverage for the following scripts:

• [x] replica_exchange_EE.py (not including functions relevant to MT-REXEE)
• [x] utils/gmx_parser.py
• [x] utils/utils.py
• [x] analysis/analyze_traj.py

Note that scripts like utils/exceptions.py and analysis/analyze_matrix.py already have code coverages nearly 100%. Some future work include

• Adding unit tests for the following scripts:
  • analysis/analyze_free_energy.py
  • analysis/clustering.py
  • analysis/msm_anslysis.py
  • analysis/synthesize_data.py
• Adding regression tests for CLIs.
• Adding tests using MPI
• Adding tests relevant to multi-topology REXEE

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 86.00000% with 21 lines in your changes are missing coverage. Please review.

Project coverage is 92.34%. Comparing base (4b409bd) to head (0f9952b).

Files	Patch %	Lines
ensemble_md/analysis/analyze_matrix.py	66.66%	8 Missing :warning:
ensemble_md/replica_exchange_EE.py	73.91%	6 Missing :warning:
ensemble_md/analysis/synthesize_data.py	83.33%	5 Missing :warning:
ensemble_md/analysis/analyze_traj.py	96.96%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #37 +/- ## =========================================== + Coverage 52.95% 92.34% +39.38% =========================================== Files 7 8 +1 Lines 1571 1645 +74 =========================================== + Hits 832 1519 +687 + Misses 739 126 -613 ```

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