fix(go): a project package named like a standard-library package is not the standard library

A Go reference written through a package qualifier was dropped as a
standard-library reference whenever the qualifier matched a name in
the built-in list (errors, log, types, parser, encoding, template, ...).
The check looked at the name alone, never at what the file imports
under that name, so a project with its own package of such a name lost
nearly every call into it: harbor's errors.New(...) through its
lib/errors, prometheus's parser.Inspect(...) through promql/parser.

What the file imports now decides before the name does. A qualifier
the file imports, by its last path segment, the name goimports assumes
for an unaliased import, or an alias, from a package of one of the
project's own modules is a project package, and the reference goes on
to normal resolution. A file that imports the standard library's
package of that name, and a qualifier the file doesn't import at all,
are skipped as before.

Validation: the new test file has 7 cases, 4 of which fail on main;
all pass here, with the native kernel and with CODEGRAPH_KERNEL=0.
A/B against main: harbor 296f304 (its Go tree, 1,611 Go files) +2,889
edges, prometheus a2fda0e +454, 0 removed and 0 retargeted on both,
nodes unchanged. Every added edge was checked against its source: the
line spells qualifier.Name and the file imports the target's package
directory under that qualifier from inside the module (3,343 of
3,343), and a sample of 10 was read by eye. gin and cobra, and the
controls express and flask, are byte-identical. Index CPU on harbor,
median of 3 interleaved: 40.0 s on main, 39.9 s here.

Original PR #2368 by @danusha2345.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/resolution/index.ts

@@ -3307,6 +3307,16 @@ export class ReferenceResolver {
       !PYTHON_BUILT_IN_TYPES.has(ref.referenceName.slice(0, dot));
   }
 
+  /**
+   * True when the Go file imports `qualifier` — by its last path segment or
+   * an alias — from a package of one of the project's own modules.
+   */
+  private isGoProjectPackage(ref: UnresolvedRef, qualifier: string): boolean {
+    return this.context
+      .getImportMappings(ref.filePath, ref.language)
+      .some((imp) => imp.localName === qualifier && this.context.getGoPackageDir?.(imp.source, ref.filePath) != null);
+  }
+
   /**
    * Check if reference is to a built-in or external symbol
    */
@@ -3401,7 +3411,9 @@ export class ReferenceResolver {
     // Go standard library packages — refs like "fmt.Println", "http.ListenAndServe", etc.
     if (ref.language === 'go') {
       const dotIdx = name.indexOf('.');
-      if (dotIdx > 0) {
+      // What the file imports decides before the name does: a project package
+      // may be called `errors`, `log` or `types` too.
+      if (dotIdx > 0 && !this.isGoProjectPackage(ref, name.substring(0, dotIdx))) {
         const pkg = name.substring(0, dotIdx);
         // Not a local bound from a type assertion that is named like one:
         // grpc-go's `parser.ParseConfig(…)` after `parser, ok :=