feat(nimbus): add validation to nimbus review serializer for targeting context fields within version range

[moibra05]

Because

• Targeting configs were not validated against versioned targeting context fields, allowing JEXL expressions to reference fields that may not exist across the selected version range

This commit

• Adds version-range validation for targeting config JEXL expressions during experiment review
• Extracts referenced identifiers from the JEXL expression and validates them against targeting context fields for all versions in the selected range
• Reports unsupported fields with specific version breakdowns when they are only partially available

Fixes #14925

[jaredlockhart]

This is so so so sick I'm so pleased with this. Very well written, very clear, very idiomatic with the project patterns, very clearly and well tested.

Try to do the test fixture file approach. If it's a nightmare then we can fall back to mocking but it's worth at least trying to set it up now.

Great job @moibra05 🙏 🎉

[jaredlockhart]

Oh then we should pull this out into a utility somewhere since we're also doing it here:

experimenter/experimenter/experimenter/targeting/tests/test_targeting_configs.py

Lines 69 to 80 in d34c14c

	extracted_root_fields = set()
	for subexpr in collect_exprs(targeting_config.targeting):
	try:
	json.loads(subexpr)
	continue
	except json.JSONDecodeError:
	if subexpr.startswith("."):
	continue
	extracted_root_fields.add(subexpr.partition(".")[0])
	unknown_fields = extracted_root_fields - valid_fields

[jaredlockhart]

Set logic is the greatest thing ever 💯 💯 💯

[jaredlockhart]

I'm not sure mocking out the function calls here is the right way to do this. Usually we follow a pattern of having test fixture data and pointing the loader at it and forcing it to reload and then letting all the logic flow naturally. I'd say see if you can do that rather than mocking it out at the function level.

[jaredlockhart]

Yeah exactly like we could put these in fixture files and have the loader pick them by mocking out the file path.

[jaredlockhart]

And then we should be able to setup some dummy test targeting configs.