Reduce size of MicroProfiler

[andresovela]

The MicroProfiler class has these buffers:

const char* tags_[kMaxEvents];
uint32_t start_ticks_[kMaxEvents];
uint32_t end_ticks_[kMaxEvents];

struct TicksPerTag {
  const char* tag;
  uint32_t ticks;
};

TicksPerTag total_ticks_per_tag[kMaxEvents];

We need 20 bytes per event, so an instance of MicroProfiler uses 80 KB of RAM, even if the model you're profiling has only a few nodes.

[github-actions]

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[andresovela]

#2724 is still open