Add a block type event

[LasmarKhalifa]

The current formatting chosen is one of 3 options that we could decide to go with for this change.

Different formatting choices we can have:

1.

2.

3.

I think option 2 is the cleanest one, but open to other opinions.

[LasmarKhalifa]

• use block events for llm stats #902
• Use block events in Pi agent cogs #901
• Use block events in chat cogs #900
• Use block events in claude #899
• Add a block type event #898 👈 (View in Graphite)
• Repeat log prefix on each line of multi-line output #893
• main

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