Clean up the trace format

[bbyalcinkaya]

Based on the review feedback that the record "kind" had to be inferred from each record's shape.

• Added a kind field to every trace record. "instr" for per-instruction traces, or the operation name (hostCall, contractData, addObject, callContract, endWasm) for Soroban VM operations, so consumers can dispatch without inspecting shape.
• Removed the now-redundant instr array from Soroban VM operations (it just repeated kind) and gave its operands proper names instead of positional array slots: hostCall now has module/function, contractData now has operation/durability.
• Removed pos from Soroban VM operations, since it was always null there; kept only on instruction records, where it's a real byte offset.
• Renamed "Soroban VM events" to "Soroban VM operations" throughout, to avoid confusion with actual Soroban contract events.
• Updated docs/tracing.md to document the new format, with a runnable komet run + jq examples section.