[MAINTENANCE] Ensure that validation definitions and checkpoints save before running

[cdkini]

Ensure that ValidationDefinition and Checkpoint persist themselves to their respective stores at the start of their run methods (if they haven't already been saved). This will ensure that invariably, we will have references to them in the DB and ensure that any foreign keys generated in the result object will point to real data.

• [x] Description of PR changes above includes a link to an existing GitHub issue
• [x] PR title is prefixed with one of: [BUGFIX], [FEATURE], [DOCS], [MAINTENANCE], [CONTRIB]
• [x] Code is linted - run invoke lint (uses ruff format + ruff check)
• [x] Appropriate tests and docs have been updated

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