fix: do not limit P3 melting with dt

[haakon-e]

• remove dt argument from ice_melt
• update P3 melting docs
• update BulkMicrophysicsTendencies for 2M+P3
• minor formatting updates

Purpose

To-do

Content

---

• I have read and checked the items on the review checklist.

[haakon-e]

This change is part of the following stack:

• docs: improve formatting, fix typo #679
  • fix: do not limit P3 melting with dt #681 ◀

_{Change managed by git-spice.}