Fix formatting to preserve annotations when program is otherwise empty

[jtran]

Before this, setting the units in a KCL file that's empty would get formatted to nothing.

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Name	Status	Preview	Updated (UTC)
modeling-app	✅ Ready (Inspect)	Visit Preview	Feb 7, 2025 9:53pm

[franknoirot]

I confirmed that Nightly blows away the following KCL on formatting:

@settings(defaultLengthUnit = cm)
      // hi hi hi

and it doesn't on your branch. I feel comfortable approving. Thanks!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.05%. Comparing base (67e60cb) to head (b3acb34).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5310      +/-   ##
==========================================
+ Coverage   86.04%   86.05%   +0.01%     
==========================================
  Files          92       92              
  Lines       33250    33284      +34     
==========================================
+ Hits        28609    28643      +34     
  Misses       4641     4641              

Flag	Coverage Δ
wasm-lib	86.05% <100.00%> (+0.01%)	⬆️

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