tracehandler: Allow to disable tracehandler cache

[nsavoire]

If a zero cache size is provided to the tracehandler, the cache is completely disabled.

Rationale

Tracehandler cache is using a large amount of memory for almost no CPU benefit (disabling it did not result in a noticeable CPU increase).

[fabled]

I am also working to convert the trace cache from trace to frame based thing. It should improve its usefulness, and also allow smaller sizes to be more efficient.

Perhaps it still is beneficial to allow disabling it if needed.

[florianl]

tracehandler used to be an essential tool for the time, when counters where increased and reported for repeated stacks. With the current design, this is no longer the case. For on-CPU profiling, we also see hardly repeated stacks (usually there are differences in the leaf frames). Only for off-CPU profiling and [u,k]probe profiling, we could benefit from tracehandler and its caching.
With a focus on on-CPU profiling, maybe it is best to remove tracehandler as intermediate step and reduce also the complexity.