Add soft blur option

[spicer1]

I tested the soft-blur option using this code (OPZIONE 3):

Can you add this option (soft-blur) to main branch? The blur fades around the edge of the ellipse, making the image softer.

def draw_det(
[....]
    elif replacewith == 'blur':
        bf = 2  # fattore di blur
        blurred_box = cv2.blur(
            frame[y1:y2, x1:x2],
            (max(1, (x2 - x1) // bf), max(1, (y2 - y1) // bf))
        )

        if ellipse:
            h_roi, w_roi = y2 - y1, x2 - x1
            yy, xx = np.meshgrid(np.linspace(-1, 1, h_roi), np.linspace(-1, 1, w_roi), indexing='ij')
            rr = np.sqrt(xx**2 + yy**2)

            # ==========================================================
            # OPZIONE 0: Ellisse completamente sfocata (codice iniziale)
            # mask = np.zeros_like(rr)
            # cv2.ellipse(
            #     mask, (w_roi // 2, h_roi // 2),
            #     (w_roi // 2, h_roi // 2), 0, 0, 360, 1, -1
            # )
            # ==========================================================

            # ==========================================================
            # OPZIONE 1: Radiale lineare
            # mask = np.clip(1 - rr, 0, 1)
            # ==========================================================

            # ==========================================================
            # OPZIONE 2: Radiale quadratica
            # mask = np.clip(1 - rr**2, 0, 1)
            # ==========================================================

            # ==========================================================
            # OPZIONE 3: Plateau centrale (ATTIVA DI DEFAULT) - soft blur
            inner_radius = 0.6
            outer_radius = 1.0
            mask = np.ones_like(rr)
            mask[rr > inner_radius] = 1 - (rr[rr > inner_radius] - inner_radius) / (outer_radius - inner_radius)
            mask = np.clip(mask, 0, 1)
            # ==========================================================

            mask = mask[:, :, np.newaxis]  # broadcast su canali RGB

            roibox = frame[y1:y2, x1:x2]
            roibox = (blurred_box * mask + roibox * (1 - mask)).astype(np.uint8)
            frame[y1:y2, x1:x2] = roibox

grazie