Add retry wrapper

As I saw in older issues, you don't want to implement a retry framework inside the library, because it's hard to implement it right. Because you don't know when you can retry a network error and when not. And I totally agree with you, because consistency of the data is a very important thing.
But it can be implement at the application level, because it actually knows the nature of the query: it it a read only query or it's an idempotent write and it's safe to retry it.
Many applications would benefit from the retry logic, because it adds a lot resilience to your application.

Why not to introduce some kind of a wrapper around the library, where you set all your retry settings during the initialization. And after, when you call any query you just pass a flag whether the query is retryable or not. if it's false the wrapper just call the underlying library method, if it's true it applies the retry logic on some set or errors.

No file, test, or entry point is named. Start by reviewing pgx's existing query methods and error behavior, then define the wrapper API, retry settings, retryable errors, and query flag; done means the design and behavior are specified well enough to implement and validate.