Optimize Network Manager to not need synchronization

Removes synchronization from sending packets
Makes normal packet sends no longer need to be wrapped and queued like it use to work.
Adds more packet queue immunities on top of keep alive to let the following scenarios go out
without delay:
  - Keep Alive
  - Chat
  - Kick
  - All of the packets during the Player Joined World event

Hoping that latter one helps join timeout issues more too for slow connections.

Removes processing packet queue off of main thread
  - for the few cases where it is allowed, order is not necessary nor
    should it even be happening concurrently in first place (handshaking/login/status)

Ensures packets sent asynchronously are dispatched on main thread

This helps ensure safety for ProtocolLib as packet listeners
are commonly accessing world state. This will allow you to schedule
a packet to be sent async, but itll be dispatched sync for packet
listeners to process.

This should solve some deadlock risks

This may provide a decent performance improvement because thread synchronization incurs a cache reset
so by avoiding ever entering a synchronized block, we get to avoid that, and packet sending is a really
hot activity.

Spigot-Server-Patches/Optimise-entity-hard-collision-checking.patch

@@ -11,7 +11,7 @@ Less crammed entities are likely to show significantly less benefit.
 Effectively, this patch optimises crammed entity situations.
 
 diff --git a/src/main/java/net/minecraft/server/Chunk.java b/src/main/java/net/minecraft/server/Chunk.java
-index 696634ebf5..00dd21205d 100644
+index 33456b0bb42..750fb07756f 100644
 --- a/src/main/java/net/minecraft/server/Chunk.java
 +++ b/src/main/java/net/minecraft/server/Chunk.java
 @@ -0,0 +0,0 @@ public class Chunk implements IChunkAccess {
@@ -88,7 +88,7 @@ index 696634ebf5..00dd21205d 100644
          }
          if (entity instanceof EntityItem) {
 diff --git a/src/main/java/net/minecraft/server/Entity.java b/src/main/java/net/minecraft/server/Entity.java
-index 0dbe2dce11..324fd07bce 100644
+index 0dbe2dce111..324fd07bcee 100644
 --- a/src/main/java/net/minecraft/server/Entity.java
 +++ b/src/main/java/net/minecraft/server/Entity.java
 @@ -0,0 +0,0 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
@@ -133,7 +133,7 @@ index 0dbe2dce11..324fd07bce 100644
          this.id = Entity.entityCount.incrementAndGet();
          this.passengers = Lists.newArrayList();
 diff --git a/src/main/java/net/minecraft/server/EntityEnderDragon.java b/src/main/java/net/minecraft/server/EntityEnderDragon.java
-index 5bf99e0028..aecdaacfc7 100644
+index 5bf99e0028b..aecdaacfc7d 100644
 --- a/src/main/java/net/minecraft/server/EntityEnderDragon.java
 +++ b/src/main/java/net/minecraft/server/EntityEnderDragon.java
 @@ -0,0 +0,0 @@ public class EntityEnderDragon extends EntityInsentient implements IMonster {
@@ -145,7 +145,7 @@ index 5bf99e0028..aecdaacfc7 100644
          return this.children;
      }
 diff --git a/src/main/java/net/minecraft/server/IEntityAccess.java b/src/main/java/net/minecraft/server/IEntityAccess.java
-index 4157e50e4d..5135308fb6 100644
+index 4157e50e4d9..5135308fb61 100644
 --- a/src/main/java/net/minecraft/server/IEntityAccess.java
 +++ b/src/main/java/net/minecraft/server/IEntityAccess.java
 @@ -0,0 +0,0 @@ public interface IEntityAccess {
@@ -178,7 +178,7 @@ index 4157e50e4d..5135308fb6 100644
  
              return stream.filter(axisalignedbb1::c).map(VoxelShapes::a);
 diff --git a/src/main/java/net/minecraft/server/World.java b/src/main/java/net/minecraft/server/World.java
-index c8619af2cf..899c535c40 100644
+index c8619af2cf4..899c535c405 100644
 --- a/src/main/java/net/minecraft/server/World.java
 +++ b/src/main/java/net/minecraft/server/World.java
 @@ -0,0 +0,0 @@ public abstract class World implements GeneratorAccess, AutoCloseable {