Keep PO parser fuzzy state instance-local

[OskarEichler]

Summary

Keep the ignore_fuzzy parse option on each PoParser instance.

The process-global variable lets concurrent parser instances overwrite one another's policy, producing cross-thread fuzzy-entry behavior.

Verification

• focused external concurrent parser model
• 1,607 base-suite runs / 2,674 assertions
• 1,888 Rails-suite runs / 3,020 assertions
• all 46 shipped Ruby files pass syntax checks

[radar]

Thanks!