fix: allow duplicate readback/config

[shaikhhasib]

Description

Allow duplicate readback_address and config_address while keeping setpoint_address unique.

Normalize blank optional addresses to NULL during PV creation/import.

Add bulk import pre-checks for duplicate/existing setpoints with batching to avoid Postgres parameter limits.

Add tests for blank optional addresses and duplicate readbacks.

Add migration to drop unique constraints on readback/config and keep non-unique indexes.

Motivation

CSV import of large datasets was failing with 500 errors due to uniqueness violations on optional address fields.
This change makes the uniqueness rules match the desired behavior (setpoint unique, readback/config allowed to repeat) and prevents hard DB errors during bulk import.

Where Has This Been Documented?

Code Comment

Screenshots

NA

Pre-merge checklist

• Code works interactively
• Code contains descriptive docstrings
• New/changed functions and methods are covered in the test suite where possible
• Test suite passes locally
• Test suite passes on GitHub Actions