chore(flags): Add some tests for flag matching

[danielbachhuber]

Changes

Adds some tests for flag matching behavior in support of PostHog/posthog-js#1519

How did you test this code?

CI should pass.

[neilkakkar]

flyby, you should instead copy these tests into posthog-js: https://github.com/PostHog/posthog/blob/master/rust/feature-flags/tests/test_flag_matching_consistency.rs#L12

All SDKs have these tests, so you'd also find the js version already written in posthog-js-lite - this ensures the hashing is consistent across SDKs doing local evaluation.

[neilkakkar]

(or, well, these can be in addition to the above^ if you're trying to check something different here :)

[posthog-bot]

This PR hasn't seen activity in a week! Should it be merged, closed, or further worked on? If you want to keep it open, post a comment or remove the stale label – otherwise this will be closed in another week. If you want to permanentely keep it open, use the waiting label.

[danielbachhuber]

Punting on this for now, see PostHog/posthog-js#1519 (comment)