Use fine-grained deltas for changing the randomization of stars and polygons

Steps to reproduce:

• Draw a star.
• In the top toolbar, focus the 'Randomized' field.
• Press Up and Down.

What happened?

• Randomization changes by +1 and -1.

What should have happened?

• Randomization changes by +0.01 and -0.01, as the effects are quite drastic.
• Same for the 'Rounded' field. There are some interesting shapes you can create with these parameters, therefore it might make sense to not accelerate the change rate when keeping the +/- buttons pressed.

Version info

Inkscape 1.3-beta (cedbd6c6ff, 2023-05-28)

    GLib version:     2.76.3
    GTK version:      3.24.38
    glibmm version:   2.66.6
    gtkmm version:    3.24.7
    libxml2 version:  2.10.4
    libxslt version:  1.1.38
    Cairo version:    1.17.7
    Pango version:    1.50.14
    HarfBuzz version: 7.3.0

    OS version:       Windows 11 22H2