Improve "make root node" trace attributes (#92941)
### What?
Improve the trace span attributes for "make root node" operations in the
turbo-tasks backend. Instead of recording only the raw `task_id`, the
spans now include a human-readable task description (type name + task
ID) via `debug_get_task_description`.
### Why?
When profiling or debugging with tracing tools, raw task IDs are opaque
and require additional lookups to understand which task is being
processed. Including a human-readable task description (e.g. `TaskId(42)
MyFunction(args...)`) makes traces immediately actionable.
Two spans were affected:
- `"make root node for strongly consistent read"` in `backend/mod.rs`
- `"make root node for removing collectible"` in
`backend/operation/update_collectible.rs`
### How?
- Added `debug_get_task_description` method to the `ExecuteContext`
trait in `operation/mod.rs`
- Implemented it on `ExecuteContextImpl` by delegating to the existing
`backend.debug_get_task_description` method (already used in other
tracing spans)
- Replaced `%task_id` (which formats only the ID) with `task =
self.debug_get_task_description(task_id)` / `task =
ctx.debug_get_task_description(task_id)` in both span definitions
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