Adaptive nsegs

[jeremyleung521]

Issue Number

Describe the changes made

This PR allows one to dynamically adjust the bin target count (target number of segments per bin) with a multiplier.
This multiplier can be determined in two different ways and is always capped by max_target_count_multiplier:

• Sample Density: Adjust target count based on "sample density", which is a value dictating the number of segments/unit progress coordinate volume. ("volume" in terms of progress coordinate dimensions. It could effectively be "length" for 1D PC, "area" for 2D PC etc.)
• Total number of segments: Adjust target count such that it's as close to the maximum number of trajectories per simulation (n_bins * segments_per_bin).

These two cannot used simultaneously.

To turn this on, you can use the following options.

west:
  system:
    system_options:
      # Number walkers per bin
      bin_target_counts: 5
      sample_density: False  # Turn this on to adjust based on sample density
      ideal_sample_density: 25  # Number of segments per PC unit volume
      force_max_target_counts: True  # Turn this on to adjust based on target count
      max_target_count_multiplier: 3  # Cap out how large the multiplier can be.

Goals and Outstanding Issues

• [ ]

Major files changed

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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