FIX: signal prec default

[ZLLentz]

Description

When the core (signal) plugin receives a floating point value with no precision information or nonsensical precision information, set the precision metadata to a sensible default.

Manual precision setting at the device/signal level is still supported fully.

Motivation and Context

By default, we had/have the following cases:

Before: 0.23 displays as 0

After: 0.23 displays as 0.230

How Has This Been Tested?

I added targeted unit tests

Works interactively with state_velo, which is the signal that led us to this issue:

Where Has This Been Documented?

Release notes

Pre-merge checklist

• [x] Code works interactively
• [x] Code contains descriptive docstrings, including context and API
• [x] New/changed functions and methods are covered in the test suite where possible
• [x] Code has been checked for threading issues (no blocking tasks in GUI thread)
• [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]

closing/reopening to cycle CI

[ZLLentz]

Made the requested change and also adjusted the test slightly to nitpick the naming/annotations and cover a case that I accidentally removed