Add message per second rate to Trading Mock Server

### Describe the feature

Trading Mock Server needs to log how much message per second it processes in the console.

### Use Case

When multiple testing clients run, it's hard to aggregate results from each client to show how much the total load is on the exchange side. Therefore, the mock client should print out how many requests it responds to in the console log

### Proposed Solution

log the message per second metric everytime mock server processes 50K messages.
For example if 150K request is sent then we should expect to see 3 log on the console showing how much message is processed per second

### Other Information

_No response_

### Acknowledgements

- [ ] I may be able to implement this feature request
- [ ] This feature might incur a breaking change

### Language

Rust

Locate the Trading Mock Server's message-processing and console-logging entry points first. Add the metric at each 50K-message threshold, then verify the console output for 50K and 150K processed messages, which should produce one and three logs respectively.

Written by the indexing model from the issue text.