Test how fast PGEN can consume the table

[tomtrafford]

First step of development for #61.

We would like to understand and test the current functionality of the PGEN table. We want to write a large PGEN table and document the metrics of how fast the table is consumed.

[tomtrafford]

After having discussed this with @coretl
We want to test the capabilities of writing a table through the DMA interface. To do this we would want to measure how long it takes to write a very large table (10 million points) to the server. The best interface for this would be using the PandABlocks python client, testing in both base64 and ascii formats.

We want to check how this affects the CPU usage of the PandA server during this process, and ensure that if we write points to PGEN at 1MHz that PCAP can capture them at 1MHz.