Fun fact a toaster in water probably won’t kill you, I mean it could obviously but it’s more likely that the electricity goes straight to the ground within the toaster, and slowly heat up the water, I wouldn’t try it but interesting nonetheless.
A GFCI, yes, but regular circuit breaker won't stop it from killing you, it's primarily there to keep the house wiring from melting and burning down the house :) You just need 6 milliamps across the heart to f you over.
They've been code in the US since 1975, yet I've been in a surprising number of bathrooms from houses in the '80s that did not have GFCI protection. We really didn't start seeing a lot of GFCI circuit breakers here until the 2000s before then it was all just single protected outlets