The other issue is that Caseta in-wall dimmers don’t work that way. Tapping the top button on a Caseta device will not result in a “button” event being sent to ST. The attached load will be set to 100%. That’s just the way that the in-wall dimmers work. They can’t be configured to work any other way.
The native ST Lutron integration doesn’t support Pico’s, but there are community integrations that do. They require the pro bridge though because they connect through Telnet to the Lutron Pro bridge. And you could implements a double-tap function in a custom DTH. The Lutron bridge publishes only 2 events for every button, pushed and released. So, your DTH would have to add code to destinguish between push, hold and double-tap. These integrations require a NodeJS server running locally though.