ENH: XPP calc namespace hotfix

[ZLLentz]

Description

In #375 and in xpp3 dev there are some updates to the calc namespace. xpp3 dev is slightly ahead in some ways and slightly behind in some others.

In this PR, I:

• Start from #375
• Manually include the additions in xpp3
• Simplify
• Update pcdscalc pin to ensure we have latest

Motivation and Context

• See #375 for info
• I'm trying to get this in as part of https://jira.slac.stanford.edu/browse/ECS-6333
• I didn't merge the other PR because xpp3 had elements missing from #375

How Has This Been Tested?

Where Has This Been Documented?

Pre-release notes and PR only

Pre-merge checklist

• [x] Code works interactively (a real hutch config file can be loaded)
• [x] Code contains descriptive docstrings, including context and API
• [x] New/changed functions and methods are covered in the test suite where possible
• [x] Test suite passes locally
• [x] Test suite passes on GitHub Actions
• [x] Ran docs/pre-release-notes.sh and created a pre-release documentation page
• [x] Pre-release docs include context, functional descriptions, and contributors as appropriate

[ZLLentz]

This supersedes #375

[ZLLentz]

Vincent is on vacation through the end of them month, so I'm going to merge this now and ask him to double-check when he gets back. But this should be pretty uncontroversial.