refactor: replaced 'os.path.join()' uses with 'pathlib.Path' / syntax

[soto-raul]

Description

This PR closes #1627.
As per the issue's description, in this PR most instances of os.path.join on strings with the corresponding / syntax for pathlib.Path objects. For example:

# BEFORE
full_path = os.path.join(root_dir, dir_path)

# AFTER
full_path = Path(root_dir) / dir_path # After

However, files with the prefix test_ were not considered for this refactor; therefore, they maintained the usage of os.path.join

Files Changed

• install/find_mpi.py
• libensemble/executors/executor.py
• libensemble/manager.py
• libensemble/resources/resources.py
• libensemble/tests/run_tests.py
• libensemble/tests/scaling_tests/forces/forces_adv/forces_simf.py
• libensemble/tests/scaling_tests/forces/forces_adv/forces_support.py
• libensemble/tests/scaling_tests/forces/forces_adv/run_libe_forces.py
• libensemble/tests/scaling_tests/forces/forces_adv/run_libe_forces_from_yaml.py
• libensemble/tests/scaling_tests/forces/forces_gpu/run_libe_forces.py
• libensemble/tests/scaling_tests/forces/forces_gpu_var_resources/run_libe_forces.py
• libensemble/tests/scaling_tests/forces/forces_multi_app/run_libe_forces.py
• libensemble/tests/scaling_tests/forces/forces_simple/run_libe_forces.py
• libensemble/tests/scaling_tests/forces/forces_simple_with_input_file/run_libe_forces.py
• libensemble/tests/scaling_tests/forces/globus_compute_forces/forces_simf.py
• libensemble/tools/parse_args.py
• libensemble/tools/tools.py

Additional Notes

It would be a good idea to consider replacing other uses of the os module with their pathlib equivalents. For example, os.path.exists() could be replaced by Path.exists().

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.30%. Comparing base (155c234) to head (04a7dd8).
⚠️ Report is 5 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1637      +/-   ##
===========================================
+ Coverage    78.19%   78.30%   +0.11%     
===========================================
  Files           76       76              
  Lines         7580     7584       +4     
  Branches      1119     1119              
===========================================
+ Hits          5927     5939      +12     
- Misses        1452     1460       +8     
+ Partials       201      185      -16     

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