Try to fix invalid sessions received when reconnecting to the Gateway

[abitofevrything]

Description

A few users have been experiencing INVALID_SESSION events after their client reconnects to the Gateway, for no apparent reason. Testing reveals this is pretty easy to reproduce simply by cutting the client's internet connection and reconnecting it once the reconnect loop starts (it's also easier to reproduce with lower ping intervals).

A theory I have as to why this happens is that when we disconnect with the intent to reconnect later (or when a ping fails, in which case we also try to reconnect), the websocket is closed with a 1000 (when we close it) or a 1001 (when a ping fails). Discord considers these "normal" close codes, and terminates the session. When we then try to resume, the session is already closed.

At least, that's my theory. For now I've removed the ping interval (since heartbeats effectively do the same thing) and changed all close codes to be non-"normal" (other than when disposing, since that is a case where we do want Discord to end the session).

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• Ran dart analyze or make analyze and fixed all issues
• Ran dart format --set-exit-if-changed -l 160 ./lib or make format and fixed all issues
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works