Fix: Restrict tip percent between 0-100%

[Vishalkumar800]

Description:
Implemented isValidTipPercent using coerceIn(0.0, 100.0) to ensure the tip percentage remains within a valid range (0 to 100).

Previously, an invalid tip percentage (e.g., negative values or values above 100) could result in incorrect tip calculations.

Adding this validation ensures that the function behaves predictably and avoids unexpected results.

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