feat: Only load bandits when new models are needed

[typotter]

Motivation and Context

As the bandit models are updated on the server with a lower frequency than the flag configuration, oftentimes, we can avoid loading bandits as we're able to reuse the versioned bandit model.

Changes

• JIT checking of whether existing bandit models are sufficient for reuse or if models need to be fetched
• Renaming of fromJson to fromArray as the method takes an associative array, not a JSON string
• Also renaming local vars from $json to $arr for increased precision

[aarsilv]

Great fast follow and I appreciate the renaming cleanup as well! 👏

Approving assuming you add in some clarifying comments as requested