refactor: use new constructor of QuantityFactory

[romanc]

Description

Prefer the new constructor of QuantityFactory over the deprecated call to QuantityFactory.from_backend(...). This removes a bunch of deprecation warnings in tests.

See NOAA-GFDL/NDSL#228 for context.

/cc @FlorianDeconinck

How Has This Been Tested?

Search and manual replace of from_backend within pyFV3. CI is still green.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas: N/A
• I have made corresponding changes to the documentation: N/A
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included: N/A
• Targeted model if this changed was triggered by a model need/shortcoming: N/A

[oelbert]

👍

[romanc]

Someone else needs to merge on my behalf, I don't have permission to do so.