Why is the Tu-204 virtually immune to wing and tail icing?
Just like Teslas, being designed in California, perform worse in ice and snow than Volvos, Russian airplane designers pay more attention to icing than Western ones, where efficiency is paramount. And you can design for icing, mainly by selecting a large leading edge radius which keeps suction peaks low. In addition, large airplanes are proportionally less susceptible to icing.
From NASA:

Wings that are thin or have sharp leading edges are more efficient ice collectors. For this reason, smaller, thin airfoils may accrete more ice faster than larger, thick airfoils. A large transport aircraft will accrete proportionally less ice than a smaller aircraft traversing the same icing environment.


Also, if the leading edge radius of the wing decreases from root to tip (as it frequently does in swept or tapered wings), the ice accretion will be proportionately greater near the tip. When contaminated with ice, wings with this design may experience flow separation at the tip before the root. Note that this is exactly opposite the way clean wings are typically designed to experience flow separation. Thus, when you fly these types of aircraft, you could lose aileron effectiveness before total wing stall, increasing the probability of an uncommanded roll and greater difficulty in regaining control.

A further factor is the thrust margin of airplanes. Being a two-engined airplane, the Tu-204 has plenty of excess thrust to compensate for the addd drag of iced wings. Since icing occurs at moderate altitudes, the thrust margin there is considerable. The same is true of the B777 and the A330, of course.
But much is left to trial-and-error. Again NASA:

Some aircraft seem to be more susceptible to airframe icing than others. The reasons for this are not well understood and probably involve multiple factors. For example, there seems to be a complicated interaction between the details of the wing design (e.g., taper ratio, twist) and its relation to the fuselage.

And in Russia icing research is well established. From the website of the Central Aerohydrodynamic Institute (TsAGII)

In Central Aerohydrodynamic Institute named after Prof. N.E. Zhukovsky (part of Zhukovsky Institute National Research Centre) the considerable attention is paid to icing effect made on aerodynamics, stability and controllability of aircraft.

The T-101 windtunnel of TsAGII in Zhukovsky is specially equipped for icing studies and has been used in the design of most Russian airplanes. I could not find a confirmation but would be surprised if the Tu-204 basic design has not been extensively studied there.