update flake.nix and add dependencies as submodules

[chirp] / ext / ziglmdb

diff --git a/ext/ziglmdb b/ext/ziglmdb
new file mode 160000 (submodule)
index 0000000..88cb74a
--- /dev/null
+++ b/ext/ziglmdb
@@ -0,0 +1 @@
+Subproject commit 88cb74a430fa9629c8127c3a866c40e79a8e4612