Unify autosim/pipeline vol_mult interface

[nagakingg]

Description

Convert int/float vol_mult input to dict format supported by pipelines.

Closes #168

Hygiene checklist

• Changelog entry
• Everything public has a Numpy-style docstring
  (modules, public functions, classes, and public methods)
• Pylint score monotonically increased
• Commit history is cleaned-up with minor changes squashed together
  and descriptive commit messages following Tim Pope's style

Cute Animal Picture

[github-actions]

Coverage report

The coverage rate went from 75.29% to 75.22% ⬇️
The branch rate is 61%.

33.33% of new lines are covered.

Diff Coverage details (click to unfold)

curvesim/sim/init.py

33.33% of new lines are covered (16.32% of the complete file).
Missing lines: 145, 181, 182, 183