The following issue is a follow-up ticket to track some remaining comments from the PR #695

• it would be neat to think about changing the exit ABI so that when tracing is enabled we always bring along a trace structure in some extra registers and can coalesce the exits.
• produce a separate file with call site -> string message mappings, and only record the call site number in the buffer
• check tracing output for expected values
• reconsider the flush macro
• Unify the hypervisors registers with the read_trace_req to not have yet another type that represents registers
• Check whether the TraceBuffer generic parameter could be replaced by a closure to improve perf