Make a central `PVValue` definition

[LowriJenkins]

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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