detect-pcre: convert unittests to FAIL/PASS APIs

[Cherrypick14]

Ticket: #6344

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Link to ticket: https://redmine.openinfosecfoundation.org/issues/6344

Describe changes:

• Replaced legacy test result handling with the FAIL/PASS macros.
• Ensured all test outcomes now consistently use the unified test convention.
• Cleaned up redundant return statements and improved readability

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[Cherrypick14]

Hi @victorjulien can I please get a review on this. I implemented the suggested feedback. Let me know if this is better now.