fix: alternate player spawning no players or networkclient player registration

[NoelStephensUnity]

This resolves the issue where using NetworkObject.InstantiateAndSpawn or NetworkSpawnManager.InstantiateAndSpawn would not properly populate the NetworkSpawnManager.PlayerObjects or the NetworkClient.PlayerObject.

Changelog

• Fixed: Issue where spawning a player using NetworkObject.InstantiateAndSpawn or NetworkSpawnManager.InstantiateAndSpawn would not update the NetworkSpawnManager.PlayerObjects or assign the newly spawned player to the NetworkClient.PlayerObject.

Testing and Documentation

• Includes integration test updates to NetworkClientAndPlayerObjectTests.ValidatePlayerObjects.
• No documentation changes or additions were necessary.