Fix resource leak pattern in DependencyGraphParser.parseLiteral()

[joshinii]

Wrap the BufferedReader in try-with-resources so it is closed even if parse() throws. StringReader.close() is currently a no-op, but this is to keep the method consistent with the rest of the codebase.

Fixes #1996

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[gnodet]

Correct and minimal conversion of parseLiteral() to try-with-resources, consistent with the same pattern already applied to parseMultiResource() in commit 16bbda7. The change is trivially safe since the underlying StringReader.close() is a no-op, but it eliminates a latent leak pattern if the reader type ever changes.

One optional follow-up opportunity: the parse(URL resource) method (lines 175-189) still uses the pre-Java-7 try-finally-catch pattern with manual null checks and a swallowed IOException. Unlike parseLiteral(), that method wraps a real InputStreamReader over resource.openStream(), so converting it to try-with-resources would be more meaningful and would complete the consistency cleanup within this file.

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Claude Code on behalf of gnodet