PCASpy: Push improvements to PVDB upstream

As a developer of an open source project I want improvements we have made to be available to other parts of my project and to the upstream developers. The `Record` and `Records` classes added in https://github.com/ISISComputingGroup/EPICS-LSICorrelator/pull/1/ will be useful to other IBEX developers using PCASpy. These were added as part of #4918, so some of the code will only be relevant to that IOC.

This ticket needs to identify which parts of that pull request are of general use and move them to a more central location. If possible, we should try and push the changes upstream to PCASpy, making them available to everyone in a later release of PCASpy.

### Acceptance criteria
- [ ] Generally useful additions to PCASpy are identified in https://github.com/ISISComputingGroup/EPICS-LSICorrelator/pull/1/
- [ ] These changes have been moved to a central location in the IBEX codebase for use in other IOCs, or have been pushed upstream
- [ ] Unit tests are added as required when the code is moved.