Make a central `PVValue` definition

# Feature Description

As a developer, I would like to be able to import `PVValue` from a central location anywhere in the project without needing to import Genie Python.

## Explanation
Genie python is a large import, and so in some cases it has been avoided to import when just the `PVValue` type is required, this has lead to multiple definitions of `PVValue` in the project, these should be removed and replaced with a central definition in `ibex-non-ca-helpers` so that if needed the type can be modified in a single location, and code duplication is avoided.

### Additional Information
As well as the changes in genie python and other locations where PVValue is defined, all imports of PVValue will need to be pointed at the new location.

# Acceptance Criteria
- [ ] `PVValue` is defined in a central location where it can easily be imported for all uses.
- [ ] All current definitions of `PVValue` and imports of them are replaced with an import of this central definition.

# How to Review
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