GUI: Adds Entry pages (BaseParameterPage, NestablePage)

[tangkong]

Description

Adds Pages for viewing and editing details for the other entry types.

• Adds BaseParameterPage which dynamically shows and hides widgets based on which fields are present (Single PV Entries)
• adds BusyCursorThread, for simple blocking work
• slightly modify the signature of open_page_slot, but make a type alias for it so we get it right in the future
• add save-button logic (save to client, disable/hide if not editable)
• Add editable flag/toggle
• complete nestable pages (Collection view, Snapshot view)
• more tests

This is currently based on top of #96 , once that's in I'll rebase one last time

Motivation and Context

#65
#66
#67
#68

How Has This Been Tested?

I'll add tests I swear

Where Has This Been Documented?

This PR

A readback (has tolerances, no rbv)

A setpoint (no tolerances, has rbv)

Widgets update based on pv type

Pre-merge checklist

• Code works interactively
• Code follows the style guide
• Code contains descriptive docstrings, including context and API
• New/changed functions and methods are covered in the test suite where possible
• Test suite passes locally
• Test suite passes on GitHub Actions
• Ran docs/pre-release-notes.sh and created a pre-release documentation page
• Pre-release docs include context, functional descriptions, and contributors as appropriate

[ZLLentz]

Did you try a few symbol variants? This one is somewhat unintuitive to me. Did something like mdi.file-document not work for some design reason?

[tangkong]

I admittedly didn't think super hard about this, my mind was thinking of Parameters as a "building block" of sorts. But a single mdi.file-document combining into a Collection (file-document-multiple) makes a lot of sense, I was blind to the obvious thing

[tangkong]

Seeking other opinions here: is this too similar?

[ZLLentz]

It's certainly a bit closer than I'd like but I'm not sure
There's also an outline variant we could try

[tangkong]

Alternate thoughts, organized as Parameter -> Collection:

• ->

• -> (an unfilled file-document to further differentiate)

There are so many icons. I think I'll just use the second option here, before I get too creative with all of this.

[ZLLentz]

I asked some questions but things look reasonable
I wasn't able to fully test myself because I couldn't get an editable entry page to appear from superscore's ui

[tangkong]

A quick icon change, then I think we can get this in