Support traces with multiple Snapshots on same offset

[aleksisch]

Some traces has multiple Snapshot with same offset. Sometimes it breaks our current check, and there's too much corner cases, apparently we can't, for example take the first one for trace exits.

[aleksisch]

Also such snapshots generates different side traces. Current formula for trace id is: parent_id + snapshot_offset + current_bytecode. But we can't distinguish snapshot in parent trace where we exited, so we can't exactly match traces child side traces with same parent snapshot offset.