You stated that "Rust is merging random syntaxes and random packages get upgraded to std lib all the time" as though it were incompatible with "being able to go to a program from 8 years ago and run it with no problems". But there's no incompatibility here. Rust adds new features at a faster rate than Go does, but it also maintains backwards compatibility ("stability without stagnation").
Sure the mainline stays clean but thats not what matters in practice.
Which also explains why you can git clone a Go library/tool and have it not building because some dependencies introduced some breaking changes in the master branch. That happened the last 3 times I wanted to fix something in a Go project.
I really don't know where this is coming from. The only package that was included into std like this is replacing the hashmap with hashbrown, and this didn't even change the public api of the standard library at all, besides improving performance of the hashmap.
The package ecosystem was so stable that go didn’t ship with a package manager (not saying it’s good but definitely a sign of relative stability).
Besides nil pointers (typesystem could do better here) and bad logic (can’t do better but language simplicity reduces this), what you’re saying is definitely not the experience of the majority. People constantly talk about being able to go to a golang program from 8 years ago and run it with no problems. Rust changes every few weeks.