Fetch analysis crate directly from the upstream git

Instead of keeping a copy of analysis, we can fetch it directly from the upstream git repository.

Note that to improve network use, a shallow copy is explicitly used (see .cargo/config.toml).

The latest version of analysis (with a small change to the Cargo.toml) makes cargo a bit buggy due to a weird dependency hole, which may be fixed in a newer version of cargo.

Furthermore, due to the cargo configuration of prusti, cargo must be configured with the -Zbindeps flags (see flake.nix).

rr_frontend/.cargo/config.toml

@@ -209,3 +209,10 @@ rustflags = [
     "-Aclippy::let_underscore_untyped",
     "-Aclippy::let_unit_value",
 ]
+
+[unstable.gitoxide]
+checkout = true
+fetch = true
+internal_use_git2 = false
+shallow_deps = true
+shallow_index = true