test/fuzz: update fuzz_until script

Summary

• add readme section on how to run fuzz_until locally, also remove CI pipeline for fuzz_until, as running it in CI is not planned
• fuzz_until.py:
  • record latest coverage increase instead of latest new path
  • run fuzzer binary directly
  • add cli flag whether to wait for 2x coverage
  • add timestamps to log lines
  • remove dictionary passing as it is not needed when corpus already exist

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Relates to https://git.picodata.io/picodata/picodata/picodata/-/issues/461 Docs follow-up: not necessary