test: improve TimingResistantEqual test coverage

[mangoostaa]

This improves the test for TimingResistantEqual by adding more relevant edge cases, including:

• Empty string vs non-empty string
• Differences at the beginning of the string
• Additional prefix/suffix length mismatch tests

These cases help ensure the function properly resists timing attacks when comparing secrets of different lengths

[DrahtBot]

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[ViniciusCestarii]

Is there a planned call site for TimingResistantEqual? Is there any place libmultiprocess would need a constant-time comparison?

[mangoostaa]

Is there a planned call site for TimingResistantEqual? Is there any place libmultiprocess would need a constant-time comparison?

You're right, currently there is no clear call site in libmultiprocess that requires constant-time comparison.
This test only improves coverage for the existing function, but I agree that without a concrete use case it might not be justified here.