What is the rate limit for vertex protocol?

Can you elaborate on the concept of a rate limit for the Vertex Protocol? Specifically, what is the purpose of implementing a rate limit, and how does it affect users and the overall network? Is the rate limit set in terms of transactions per second, or is it based on a different metric? Furthermore, is the rate limit static or does it fluctuate based on certain conditions, and if so, what are those conditions? Understanding the intricacies of the rate limit for Vertex Protocol would be instrumental in assessing its scalability and usability for various applications.