FIX: Units recognition for act_accumulate_precip

[rcjackson]

What changed

2-4 bullets in plain language.

• The units were not being properly recognized for accumulate_precip.
• Units that require a conversion from mm/hr to mm/min can be in many forms (i.e. "mm/hour"). LDQUANTS has its accumulations in "mm/hour"

Why

1-2 lines on the user/problem impact.

• Any LDQUANTS accumulations were too high by a factor of 60.

Issues closed

List issue references this PR closes (for example: Closes #123, Fixes #456).

Validation

Mark each item as done or N/A. Add one short evidence line for each item.

• I ran pre-commit or ruff

• I ran tests and/or added tests

AI usage & manual verification

If AI tools were used, complete this section.

• AI used: yes
• Model/tooling: Codex/GPT 5.6-Luna
• Tasks delegated to AI: Finding the error while making a radclss notebook. Code inserted manually.
• Manual verification performed: Yes

Use Xarray Dataset naming

When adding dataset usage to the code use ds for Datasets and da for
DataArrays

Impact note (optional): breaking behavior, scientific output shift, or user-visible behavior.