make `init` return the allocated loop

make `init` return the allocated loop, as it is done in `Allocator` itself.

file: pkgs/cli/src/main.zig

_Originally posted by @gballet in https://github.com/blockblaz/zeam/pull/36#discussion_r2250132621_

Open pkgs/cli/src/main.zig and find init alongside the Allocator implementation. Compare how Allocator returns its allocated loop, then update init so its result exposes the allocated loop. Done means init returns the loop consistently with Allocator; no test file is named in the issue.

Written by the indexing model from the issue text.