Implement -max_total_time in the standalone fuzz harness

[alexreinking]

We've been running the fuzz tests for too much time in CI because the limits imposed on runtime were left to future work in #9050. We now stop running after 5 minutes, as anticipated.

Checklist

• Tests added or updated (not required for docs, CI config, or typo fixes)
• Commits include AI attribution where applicable (see Code of Conduct)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
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Additional details and impacted files

@@           Coverage Diff           @@
##             main    #9161   +/-   ##
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  Coverage        ?   69.26%           
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  Files           ?      254           
  Lines           ?    78216           
  Branches        ?    18712           
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  Hits            ?    54176           
  Misses          ?    18513           
  Partials        ?     5527           

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