chore: fix gossipsub benchmarks

[dozyio]

Description

Fix gossipsub benchmarks so that they can run

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if necessary (this includes comments as well)
• I have added tests that prove my fix is effective or that my feature works

[dozyio]

Might want to migrate off benchmark.js as it hasn't been updates in a long while

[tabcat]

i think tinybench is new standard https://github.com/tinylibs/tinybench

[dozyio]

Thinking to get this one in as it matches the rest of the repo and then migrate all off benchmark.js

[tabcat]

• Heartbeat was timing the publish, not heartbeat(). The migration folded
  the old untimed beforeEach publish into the timed fn, so it measured
  ~275 ms/op instead of ~3.66 ms/op. Moved it to a one-time warm-up so it times
  heartbeat() alone.
• Node teardown — the 50 nodes were never stopped, so their timers kept the
  process alive and the run hung after finishing. Added stop().
• Deduped runBenchmark → test/utils/benchmark.ts (was copied in all 4 files).
• @types/benchmark added, dropped the @ts-expect-error.
• mocha → aegir test -t node (mocha wasn't a direct dep), kept --exit
  as a safety net.