fix(flags): Add appropriate timeouts, fix some other misc things

[neilkakkar]

This PR does a few things:

1. Add a feature_flag_request_timeout_seconds configuration option, defaulting to 3s to control flag timeouts
2. Gets rid of a lot of error spew, instead allows passing in an on_error proc so users can decide what to do with errors
3. Unifies calling sites such that everything doesn't call the /decide endpoint directly, but via get_all_flags_and_payloads which in turn does all necessary error handling. Before this, getting payloads would always throw :/
4. Noticed as a result of above^ that we were sometimes inefficiently going to decide. The test updates where I add a second feature flag key for beta-feature2 reflect that, since previously this would go to decide, but now it wouldn't, which is infact the ideal thing to do. (and thus to test the old flow we need an extra flag that is present but can't be locally evaluated).

Noticed while doing this that the above problem exist in posthog-python as well, will update that too

[mariusandra]

Some ruby thoughts, but 🚢