improv(progress_bar): unify indeterminate animations

[git-f0x]

• I have disclosed use of any AI generated code in my commit messages.
  • If you are using an LLM, and do not fully understand the changes it is making to the code base, do not create a PR.
  • In our experience, AI generated code often results in overly complex code that lacks enough context for a proper fix or feature inclusion. This results in considerably longer code reviews. Due to this, AI authored or partially authored PRs may be closed without comment.
• I understand these changes in full and will be able to respond to review comments.
• My change is accurately described in the commit message.
• My contribution is tested and working as described.
• I have read the Developer Certificate of Origin and certify my contribution under its conditions.

This makes both Linear and Circular have effectively the same animation (kind of matching how linear indeterminates usually look).

Also does some deduplication in circular with a few closures and avoids a divide by 0 when cycle_duration is set to 0 (matching the behavior in the rotation_duration comment).

Before:

Screencast_20260419_172047.webm

After:

Screencast_20260419_201908.webm

The original animation can be replicated with tweaks to min and wrap lengths (setting them to 0.0 and 1.0, respectively), so I wonder if it might be worth having methods for setting those?

The second commit adds animations between progress states:

Screencast_20260420_135309.webm

Screencast_20260420_135243.webm

Edit: I've renamed rotation_duration and traversal_duration to period in order for both to have a similar API. Not sure if that's the best name (maybe sweep_duration?).