Allow w_init to save bin_mapper stuff to iteration 1

[jeremyleung521]

Issue Number

Describe the changes made

Logic for w_init is different to w_run in that it doesn't save the bin mapper for iteration 1. This new PR will result in a behavior where bin_target_count dataset and corresponding bin_topology hash/pickle will be created for iteration 1.

Goals and Outstanding Issues

• [x] Make iteration 1 more consistent with later iterations

Major files changed

• [x] src/westpa/core/sim_manager.py

Status

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

Additional context