update flake lock, add flake diff, add evaluation json

Signed-off-by: ahuston-0 <aliceghuston@gmail.com>

flupdt/flake_diff.py

@@ -0,0 +1,30 @@
+"""Utility to diff nix derivations."""
+
+import logging
+import shutil
+
+from flupdt.common import bash_wrapper
+
+
+def compare_derivations(
+    path_to_flake: str, path_to_pre_drv: str, path_to_post_drv: str
+) -> list[str]:
+    """Gets all derivations present in a flake.
+
+    :param path_to_flake: path to flake to be checked
+    :returns a list of all valid derivations in the flake
+    :raises RuntimeError: fails if nix is not present in the PATH
+    """
+    nvd_path = shutil.which("nvd")
+    if nvd_path is None:
+        status_msg = "nvd is not available in the PATH, please verify that it is installed"
+        raise RuntimeError(status_msg)
+    diff_output =  bash_wrapper(
+        f"{nvd_path} diff {path_to_pre_drv} {path_to_post_drv}", path=path_to_flake
+    )
+
+    logging.debug(diff_output[0])
+    logging.debug(diff_output[1])
+    logging.debug(diff_output[2])
+
+    return diff_output