Main goal of this PR is to fix the network leaks, which look like LEAK: ByteBuf.release() was not called before it's garbage-collected; I found the EnderStorage bug while I was diagnosing the CodeChickenLib (CCL) leak.

Fix OpenComputers (OC) not releasing their packets.

• Was thought to be fixed in MightyPirates/OpenComputers@6aee1d6, but closing the stream does not release the buffer because the wrong constructor was used for ByteBufInputStream.
• Fixes Potential memory leak MightyPirates/OpenComputers#3703

Fix CCL not releasing their PacketCustom payloads.

• The fix is more complicated than OC because OC uses the Forge provided FMLEventChannel but CCL tried to create their networking from scratch off of FMLEmbeddedChannel. There was a previous attempt to release the payloads, but it broke mods using the library because some packets are sent to multiple clients through vanilla methods, which means those packets need to have their payloads retained accordingly. You can actually see how this is done properly in Forge's FMLOutboundHandler.
• Fixes LEAK: ByteBuf.release() was not called before it's garbage-collected TheCBProject/CodeChickenLib#220, fixes LEAK: ByteBuf.release() was not called before it's garbage-collected. TheCBProject/CodeChickenLib#285, fixes CodeChicken PacketCustom not releasing ByteBuf xJon/Tekkit-2#43
• UTPacketCustomClientMixin and UTPacketCustomServerMixin may not be necessary, but I didn't run into any problems by including them. They release the copied payloads in PacketCustom's buf. The other mixins release the passed in payload, which was the main issue.
• Tested with EnderStorage and Draconic Evolution packets using Java arg -Dio.netty.leakDetection.level=paranoid.
• If any issues occur from this fix, they would probably crash with io.netty.util.IllegalReferenceCountExceptions.

Fix EnderStorage adding duplicate Frequency entries in TankSynchronizer.

• This was because Frequency broke the Object equality contract by overriding hashCode() but not equals().

Debugging the network pipeline is confusing 😢