SwiftQUIC: PERF: Small optimizations for the tx path

[agnosticdev]

This change is a collection of minor optimizations for the tx path. ~450 megacycles.

1. Removes the minimum capacity in TransmittedItems held in SentPacketRecord. This saves an allocation and lets packets with more than one stream frame take this allocation on-demand.

157.48 M 100.0%	-	 SentPacketRecord.init()

2. This saves a path lookup in sentPacket per-packet.

734.11 M 0.9%	106.05 M	  Recovery.InnerState.sentPacket(_:time:connection:)	
155.90 M 0.2%	-       	    specialized ManyToManyProtocolHandler.path(for:)

3. Removes a the destroy overhead of Packet, which strangely showed up as outlined destroy of SwiftTLSProtocol.SwiftTLSProtocolOptions?.

171.01 M 0.2%	25.00 M	    outlined destroy of SwiftTLSProtocol.SwiftTLSProtocolOptions?	

4. Removal of dead code
5. Collected stats once per-application burst loop instead of on each packet built.