fix(@nestjs/graphql): de-duplicate per-target metadata in TargetMetadataCollection

[yogeshwaran-c]

Summary

• Make TargetMetadataCollection's objectType, argumentType, inputType and resolver setters idempotent: when the same target's metadata is re-assigned, replace the entry in the canonical all.<kind> array in place instead of pushing a second one.

Bug

@ObjectType() registers metadata both eagerly (so getObjectTypeMetadataByTarget(...) works synchronously inside @Resolver(() => Cat)) and again through LazyMetadataStorage.store(...). Each registration goes through:

set objectType(val: ObjectTypeMetadata) {
  this._objectType = val;
  this.all.objectType.push(val);
}

So every class decorated with @ObjectType() (or @ArgsType(), which also pairs an eager + lazy registration) ended up listed twice in getObjectTypesMetadata(). The downstream generateObjectTypeDefs then ran the type-definition factory once per duplicate. addObjectTypes (Map.set) hid the resulting collision but the per-target metadata compilation, plugin metadata loading, and orphan walks still all ran twice.

The same shape applies to @ArgsType() (also eager + lazy) and to @InputType() once PickType (or other helpers) double-decorate a generated abstract class.

Fix

The setters now look up the previous value in the canonical array and replace it in place, falling back to a push only when the target has not been registered yet:

private replaceOrPush<T>(list: T[], previous: T | undefined, next: T) {
  if (previous === undefined) { list.push(next); return; }
  const index = list.indexOf(previous);
  if (index === -1) list.push(next); else list[index] = next;
}

This keeps the all.<kind> arrays as a one-entry-per-target list while still exposing the most recent metadata reference. interface already uses Map.set keyed by target and is unchanged.

Test plan

• New regression test tests/schema-builder/storages/target-metadata-set.spec.ts (fails on master; passes after the fix) covers @ObjectType and @ArgsType.
• packages/graphql Vitest run is green (the pre-existing model-class-visitor / readonly-visitor plugin snapshot failures already exist on master).
• packages/apollo e2e run (tests/e2e) passes including serialized-graph.