cmd/trace: tolerate Go 1.22+ traces with broken tails

[mknyszek]

Because Go 1.22+ traces are partitioned, it's possible to isolate broken partitions and remove them from the trace data. This is especially useful if a crash happens while tracing.

Currently cmd/trace rejects any trace that isn't completely parseable, but it could easily discard a broken trace tail and report how much of the trace it discarded.

[gopherbot]

Change https://go.dev/cl/580135 mentions this issue: cmd/trace/v2: tolerate traces with broken tails