Updates flake to fully embrace crane

Crane is different from naersk in some important ways.

The new flake structure can now be easily extended to more examples,
and should make implementation of all CI workflows much simpler.

flake.nix

@@ -29,6 +29,47 @@
         fenix' = fenix.packages.${system};
         crane' = (crane.mkLib pkgs).overrideToolchain fenix'.complete.toolchain;
         manifest = (pkgs.lib.importTOML ./Cargo.toml).package;
+
+        src = crane'.cleanCargoSource ./.;
+
+        buildExample =
+          {
+            src,
+            subdir,
+            args ? { },
+          }:
+          crane'.buildPackage {
+            inherit src;
+            cargoLock = ./${subdir}/Cargo.lock;
+            cargoToml = ./${subdir}/Cargo.toml;
+
+            postUnpack = ''
+              cd $sourceRoot/${subdir}
+              sourceRoot="."
+            '';
+          }
+          // args;
+
+        refined = crane'.buildPackage {
+          inherit src;
+          cargoTestExtraArgs = "--all-features";
+        };
+
+        refined-doc = crane'.cargoDoc {
+          inherit src;
+          cargoArtifacts = refined;
+          cargoDocExtraArgs = "--all-features";
+        };
+
+        refined-example-quickstart = buildExample {
+          inherit src;
+          subdir = "examples/quickstart";
+        };
+
+        refined-example-axum = buildExample {
+          inherit src;
+          subdir = "examples/axum";
+        };
       in
       {
         devShells.${system}.default = pkgs.mkShell {
@@ -43,10 +84,23 @@
           ];
         };
 
-        # TODO: ensure that docs and examples can be built
-        packages.${system}.default = crane'.buildPackage {
-          src = crane'.cleanCargoSource ./.;
-          cargoTestExtraArgs = "--all-features";
+        checks.${system} = {
+          inherit
+            refined
+            refined-doc
+            refined-example-axum
+            refined-example-quickstart
+            ;
+        };
+
+        packages.${system} = rec {
+          inherit
+            refined
+            refined-doc
+            refined-example-axum
+            refined-example-quickstart
+            ;
+          default = refined;
         };
       }
     );