Migrate examples to zig 0.16

Many programs in examples folder create GPA manually, but it's been removed (I'm pretty sure there was a comment in the 0.15.2 stdlib about it being removed, but I do not see that being noted in the release changelog) and can be replaced with the "Juicy init" gpa.

Just noticed that there is an open PR for that, should I close this? Though some of the PR code still uses heap GPA, and that should be replaced with DebugAllocator

Done — closing.

The examples in examples/*.zig were updated as part of the broader 0.17-dev migration in 21a7934 and use the modern var gpa: std.heap.DebugAllocator(.{}) = .init (the "juicy init") pattern you flagged. Thanks for the catch.