Update python envrc template

Completely removes the need to call a shell.nix in .envrc now (I
think)

templates

@@ -208,6 +208,10 @@ envrc-file-mode
 (python "CC=\"$(nix build nixpkgs#stdenv.cc.cc.lib --print-out-paths --no-link)\"" n
         "ZLIB=\"$(nix build nixpkgs#zlib --print-out-paths --no-link)\"" n
         "export LD_LIBRARY_PATH=\"$CC/lib\":\"$ZLIB/lib\"" n
+        "VENV_DIR=.venv/" n
+        "if [ ! -f $VENV_DIR/bin/python3 ]; then" n
+        > "nix run nixpkgs#python3 -- -m venv $VENV_DIR" n
+        "fi" n
         "source .venv/bin/activate")
 
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