feat: OnNetworkPostSpawn usage, fixing animation bug on downed players on late joins [MTTB-1512]

[fernando-cortez]

Description

This PR addresses the following:

• Fainted players were not syncing fainted state on the server, so they spawned as if they appeared alive -- now achieved by having the transition fixed in the animator, but also in code when the player was spawned
• Possible race conditions on NetworkBehaviours -- visual behaviour is now deferred to OnNetworkSpawn, ensuring that all NetworkVariable and related variables are set when visuals are initialized

Issue Number(s)

MTTB-1512

Contribution checklist

• [ N/A ] Tests have been added for boss room and/or utilities pack
• Release notes have been added to the project changelog file and/or package changelog file
• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• JIRA ticket ID is in the PR title or at least one commit message
• Include the ticket ID number within the body message of the PR to create a hyperlink
• [ N/A ] An Index entry has been added in readme.md if applicable