[fso42]

Adds first draft of mu(I) rheology

PR Checklist

Please confirm before requesting review:

• I ran pytest locally without fails
• I added/updated tests where needed
• I updated documentation where needed

Confirm before the final merge/rebase into master

• Commits are sensibly squashed and rebased onto latest master
• Standardtest run without difference (with recompiled cython code)

[qltysh]

❌ 2 blocking issues (2 total)

Tool	Category	Rule	Count
black	Style	Incorrect formatting, autoformat by running qlty fmt.	2	❌

@qltysh one-click actions:

• Auto-fix formatting (qlty fmt && git push)

[JuLa96]

closes OpenNHM/DebrisFrame#120