feature: format code blocks as they’re streaming in from AI

[jimniels]

For code blocks, it kinda stinks you don't get the code highlighting until the full code block comes in, e.g. a response might look like this:

This is a code sample from me, an AI assistant:

```javascript
var x = 0;
// a cod

Only once you get everything between the code fences ``` will it turn into an editor preview.

There's probably a way we can eagerly begin styling a code block when we see the first set of code fences by changing this regex.

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Note how chatGPT triggers a formatting a code response at the first sign of a code block:

It does now, however, do this for inline code. It waits until the final backtick