[BUG] Incorrect unit type assignment in convertValueUnit

The convertValueUnit function in src/core/units.js contains a logical error where a comparison operator === is used instead of an assignment operator =. This prevents the unit type from being correctly updated after conversion, potentially leading to inconsistent animation states when handling different CSS units.

// src/core/units.js:62
decomposedValue.t === valueTypes.UNIT; // This expression has no effect

Fixing this typo ensures the animation engine correctly tracks the value type after unit conversion.