Updates the tree by adding a value to the element at a specified index. This operation also propagates the update to subsequent elements in the tree. # Arguments `index` - The zero-based index where the value should be added. `value` - The value to add to the element at the specified index. # Returns A `Result` indicating success (`Ok`) or an error (`FenwickTreeError::IndexOutOfBounds`) if th
(&mut self, index: usize, value: T)