ref: Move packet building into conn

[rklaehn]

As suggested by @ramfox in #830 (comment)

This undoes a lot of the changes to tests that were done in the initial batching PR. The packetize and packet split iter moved to the conn.

[dignifiedquire]

I am not seeing any place where the packets are split on receiving, did you miss that piece?

[rklaehn]

I am not seeing any place where the packets are split on receiving, did you miss that piece?

I did not change anything about this. It is in process_derp_read_result. The only remaining place where PacketSplitIter is still used.

[dignifiedquire]

ahh, right :)

[dignifiedquire]

did you test performance? I assume no change?

[rklaehn]

did you test performance? I assume no change?

I did not test perf. It does the same thing, just in a different place. Same number of allocations etc.

Although to be fair I think we are not at the point where we have to worry about allocations. Hopefully we will get there eventually...