feat: Add atticd service to sgx-nixos system

This commit includes the atticd service to the sgx-nixos system. The `atticd.nix` file has been added with default configuration and the attic service has been included in imports in `default.nix`. Modifications were made in `flake.nix` and `flake.lock` to integrate attic dependencies.

systems/x86_64-linux/sgx-nixos/atticd.nix

@@ -0,0 +1,36 @@
+{ pkgs, lib, config, ... }:
+{
+  services.atticd = {
+    enable = true;
+
+    # Replace with absolute path to your credentials file
+    credentialsFile = "/etc/atticd.env";
+
+    settings = {
+      listen = "[::]:8080";
+
+      # Data chunking
+      #
+      # Warning: If you change any of the values here, it will be
+      # difficult to reuse existing chunks for newly-uploaded NARs
+      # since the cutpoints will be different. As a result, the
+      # deduplication ratio will suffer for a while after the change.
+      chunking = {
+        # The minimum NAR size to trigger chunking
+        #
+        # If 0, chunking is disabled entirely for newly-uploaded NARs.
+        # If 1, all NARs are chunked.
+        nar-size-threshold = 64 * 1024; # 64 KiB
+
+        # The preferred minimum size of a chunk, in bytes
+        min-size = 16 * 1024; # 16 KiB
+
+        # The preferred average size of a chunk, in bytes
+        avg-size = 64 * 1024; # 64 KiB
+
+        # The preferred maximum size of a chunk, in bytes
+        max-size = 256 * 1024; # 256 KiB
+      };
+    };
+  };
+}