refactor(javascript): reuse validated source-map decoding

Pass typed map objects into the codec and reuse validated TraceMap instances for regular and indexed lookups. Remove whole-map serialization, duplicate leaf decoding, an array-copy wrapper, and the unused offset-validation mode in artifact declaration collection.

Validation: source-map and browser consumer suites (126 tests), declaration tests, and artifact reconstruction boundaries pass. Section overlap checks and raw source declarations remain intact.

src/application/javascript/JavaScriptArtifactAnalysis.ts

@@ -529,7 +529,7 @@ const parseSourceMap = (
     void cause;
     return invalidSourceMap(file, "Source map is not valid JSON.");
   }
-  const maps = flattenSourceMaps(value);
+  const maps = flattenSourceMapLeaves(value);
   if (maps === undefined)
     return invalidSourceMap(file, "Source map is not a version 3 map.");
   return collectSourceMapOriginals(file, maps);
@@ -594,13 +594,6 @@ const unavailableSourceMap = (
   };
 };
 
-const flattenSourceMaps = (
-  root: unknown,
-): Readonly<Record<string, unknown>>[] | undefined => {
-  const leaves = flattenSourceMapLeaves(root);
-  return leaves === undefined ? undefined : [...leaves];
-};
-
 const invalidSourceMap = (
   file: JavaScriptArtifactFile,
   limitation: string,