⚡ Bolt: Parallelize sources JAR location

[google-labs-jules]

This PR improves performance by parallelizing the source JAR location process.

Changes:

1. Parallel Execution: Changed SourcesJarLocator.fillSourcesAttribute to use parallelStream(). This allows concurrent HEAD requests to Maven repositories to check for the existence of source JARs, which is a major bottleneck in sequential execution.
2. Thread Safety:
   • Updated SourcesJarLocator.mURLCache to ConcurrentHashMap to support concurrent access.
   • Updated GraphMemoizator to use ConcurrentHashMap and computeIfAbsent to ensure atomicity and thread safety for the memoization cache.

This change is safe as GraphMemoizator and SourcesJarLocator are now thread-safe, and HttpURLConnection instances are created per request (via ConnectionFactory which opens new connections).

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PR created automatically by Jules for task 9088058870112736945 started by @menny

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