feat(nix): also add release-max-perf package build to flake outputs

nix/packages/default.nix

@@ -5,6 +5,7 @@
 {
   perSystem =
     {
+      self',
       pkgs,
       craneLib,
       ...
@@ -13,6 +14,14 @@
       packages = {
         rocksdb = pkgs.callPackage ./rocksdb.nix { };
         default = pkgs.callPackage ./continuwuity.nix { inherit self craneLib; };
+        # users may also override this with other cargo profiles to build for other feature sets
+        #
+        # other examples include:
+        #
+        # - release-high-perf
+        max-perf = self'.packages.default.override {
+          profile = "release-max-perf";
+        };
       };
     };
 }