feat: add (incomplete) nix flake

dave.py isn't packaged yet. Will try to do this myself but dealing with
vcpkg is a bit annoying.

errornocord/arguments.py

@@ -0,0 +1,47 @@
+import argparse
+import contextlib
+import io
+
+from . import utils
+
+
+class ArgumentParser:
+    def __init__(self, command, description):
+        self.parser = argparse.ArgumentParser(
+            command,
+            description=description,
+            exit_on_error=False,
+        )
+
+    def print_help(self):
+        help_buffer = io.StringIO()
+        with contextlib.redirect_stdout(help_buffer):
+            self.parser.print_help()
+        return help_buffer.getvalue().replace(" and exit", "")
+
+    def add_mutually_exclusive_group(self, *args, **kwargs):
+        return self.parser.add_mutually_exclusive_group(*args, **kwargs)
+
+    def add_argument(self, *args, **kwargs):
+        return self.parser.add_argument(*args, **kwargs)
+
+    async def parse_args(self, message, tokens) -> argparse.Namespace | None:
+        try:
+            with contextlib.redirect_stdout(io.StringIO()):
+                return self.parser.parse_args(tokens[1:])
+        except SystemExit:
+            await utils.reply(message, f"```\n{self.print_help()}```")
+        except Exception as e:
+            await utils.reply(message, f"`{e}`")
+
+
+def range_type(string: str, lower=0, upper=100) -> int:
+    try:
+        value = int(string)
+    except ValueError as e:
+        raise argparse.ArgumentTypeError("value is not a valid integer") from e
+
+    if lower <= value <= upper:
+        return value
+
+    raise argparse.ArgumentTypeError(f"value is not in range {lower}-{upper}")