Math: Cleanup ScLERP implementation.
Math: Cleanup ScLERP implementation.

 - Use explicit conversion to `T`
 - Use `std::` for `acos, cos, sin` to avoid use of double only functions
 - Do not mutate variables in math code to avoid confusion

Signed-off-by: Squareys <0f6a03d4883e012ba4cb2c581a68f35544703cd6@googlemail.com>

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