Move prefix struct to rattler

[baszalmstra]

There is a utility struct called Prefix in the current repository. It contains high level code to interact with a conda environment on disk. It would be nice to move this to the rattler crate and add additional functionalities to it (like executing a transaction on it).

https://github.com/prefix-dev/pax/blob/7231f7ccccdb39f7e75dc3059aa6fd3abdf402ee/src/prefix.rs#L7-L8

[baszalmstra]

Im not entirely sure whether or not we should do this still. There is some functionality (like discovering installed packages) that should be moved, but the Prefix struct itself has grown to incorporate pixi specific stuff.

[ruben-arts]

Closing for now, open for to long without anything, reopen if still relevant