Make test fixtures clean up the bundle and team rows they create

[anishgirianish]

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Make the database test fixtures clean up the bundle and team rows they create, in foreign-key-safe order, so tests stop leaking them. Document the fixtures and isolation pattern.

related: #68374

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[anishgirianish]

cc: @ferruzzi

[goransh-buh]

Nice clean implementation. One minor thought: the early return could be moved up to reduce nesting. But overall this looks solid.