Fix source and source-env formatting

[132ikl]

Fixes formatting of source and source-env.

Source:

source foo
source bar
source-env fooenv
source-env barnev

Before this PR:

source foo source bar source-env fooenv source-env barnev

After this PR:

source foo
source bar
source-env fooenv
source-env barnev

[blindFS]

Acknowledged, thanks!

One thing to note here:
the latest grammar of tree-sitter-nu has better support for newline characters, we probably won't need all those append_empty_softlines for decl/stmt in the future.

Still working on topiary-nushell to support the latest parser (some whitespace issue in the way). You can check the dev branch if you have interest.

Besides, related test case modification is much appreciated. We can leave it for now, since a major shift is coming.