Hdf5 speedup

[jeremyleung521]

Issue Number. Is this pull request related to any outstanding issues? If so, list the issue number.

Describe the changes made. A clear and concise description of what the problem is and what you did to fix it. E.g. [...] was happening and I've changed [...] to fix it.

Goals and Outstanding Issues. A clear and concise list of goals (to be) accomplished.

• Generalizeable loaders for trajectory saving (mdtraj, mdanalysis and amber/netcdf)
• Template file for trajectory saving (to skip unnecessary mdtraj topology read/writes)
• Convert MDAnalysis topology to MDTraj topology

Major files changed.

• [ ]

Status.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

Additional context. Add any other context or screenshots about the pull request here.

[codecov-commenter]

Codecov Report

Attention: 93 lines in your changes are missing coverage. Please review.

Comparison is base (4934c21) 41.89% compared to head (f612ad6) 41.82%.
Report is 8 commits behind head on develop.

Files	Patch %	Lines
src/westpa/core/propagators/executable.py	14.70%	29 Missing ⚠️
src/westpa/core/trajectory.py	16.66%	25 Missing ⚠️
src/westpa/core/h5io.py	15.38%	22 Missing ⚠️
src/westpa/core/data_manager.py	46.87%	17 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #28      +/-   ##
===========================================
- Coverage    41.89%   41.82%   -0.08%     
===========================================
  Files          131      131              
  Lines        17011    17094      +83     
===========================================
+ Hits          7127     7149      +22     
- Misses        9884     9945      +61     

Flag	Coverage Δ
unittests	41.82% <24.39%> (-0.08%)	⬇️

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