Fix shard shutdown via Context

This fixes the shard shutdown via the Context. This works by setting a
"shutdown" field on the Shard struct as being true, indicating that the
Shard has shutdown. The Shard Runner detects this and requests a
shutdown from the Shard Manager.

The ideal solution here would be to add a "Shutdown" variant to
serenity::gateway::ConnectionStage, but that would be a breaking change,
so we instead need to opt for adding a new struct to gateway::Shard.

The Shard Manager has also been updated to only attempt the shutdown of
a shard if it doesn't already know for certain that it shut itself down,
which avoids an error logged saying that there was an error sending a
shutdown message to its Shard Runner.

When all shards have been shutdown (for most bots, this will only be
one), the Shard Manager will end and the Client will stop its
operations, returning thread control to the user.

0 files changed, 0 insertions, 0 deletions