[Dev UI] Improve trace view for "large" traces #4193
Description
The current trace view does not scale well for large traces. Large being defined by one of the following dimensions:
- Large traces e.g. many (deeply nested) spans
- Large spans - e.g. long LLM message history
For the span tree, the following improvements should be considered
- Draggable width
- A full width "timeline" style view, common in other tracing products
For the span details many small fixes will add up to a lot
- Improve density of headings
- "Sticky" headings
- Message rendering improvement ideas
- Collapsible messages
- Automatically collapse all "history" messages
- Partially show messages, with a "click to expand" behavior