Fix: fixed math quiz giving invalid options in some questions

[ash-heinz]

I made it so that the options for the prime number question is fixed rather than generating random numbers

📝 Description

• Added fixedOptions: when a question type has a known, constrained set of valid answers (e.g. prime uses only 1 or 2) we attach the exact options here so showQuestion() skips generateOptions() which would produce arbitrary nearby numbers that are meaningless for the question being asked.
• the only valid answers are 1 (yes) or 2 (no). using generateOptions() in the case of prime numbers would fill the remaining 2 slots with random nearby integers (e.g. 13, 11, 3) that are irrelevant and confusing as was shown in the issue.

🔗 Linked Issue

Closes #354

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📋 Contribution Checklist

• My code strictly adheres to the project guidelines (Standard library only, procedural code, clean spacing).
• I have tested my changes thoroughly on my local machine.
• GSSoC 2026: I have been formally assigned to this issue and noted it above.

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