Update to latest devenv in nix flake (#3760)

Latest version - after rewrite in Rust - just released yesterday is much
nicer and has fewer bugs.

For example, it now uses process-compose which is full screen interface
for showing running processes.

Blog post: https://devenv.sh/blog/2024/03/20/devenv-10-rewrite-in-rust/

flake.nix

@@ -4,8 +4,7 @@
   inputs = {
     nixpkgs = { url = "github:NixOS/nixpkgs/nixos-unstable"; };
     flake-utils = { url = "github:numtide/flake-utils"; };
-    # See https://github.com/cachix/devenv/issues/756
-    devenv.url = "github:cachix/devenv/v0.6.3";
+    devenv.url = "github:cachix/devenv";
   };
 
   outputs = inputs@{ self, nixpkgs, flake-utils, devenv }:
@@ -84,6 +83,7 @@
 
         postgres_port = 7000;
         mosquitto_port = 7001;
+        process_compose_port = 7002;
 
         psql = pkgs.writeShellScriptBin "teslamate_psql" ''
           exec "${pkgs.postgresql}/bin/psql" --host "$DATABASE_HOST" --user "$DATABASE_USER" --port "$DATABASE_PORT" "$DATABASE_NAME" "$@"
@@ -92,11 +92,9 @@
           exec "${pkgs.mosquitto}/bin/mosquitto_sub" -h "$MQTT_HOST" -p "$MQTT_PORT" -u "$MQTT_USERNAME" -P "$MQTT_PASSWORD" "$@"
         '';
 
-      in with pkgs; {
-        packages.default = pkg;
-        devShells.default = devenv.lib.mkShell {
+        devShell = devenv.lib.mkShell {
           inherit inputs pkgs;
-          modules = [{
+          modules = with pkgs; [{
             packages = [
               elixir
               elixir_ls
@@ -116,8 +114,6 @@
                 CoreServices
               ]);
             enterShell = ''
-              # kludge for https://github.com/cachix/devenv/issues/862
-              # export PKG_CONFIG_PATH_FOR_TARGET="$PKG_CONFIG_PATH"
               export LOCALES="${cldr}/priv/cldr";
               export PORT="4000"
               export ENCRYPTION_KEY="your_secure_encryption_key_here"
@@ -131,10 +127,17 @@
               export RELEASE_COOKIE="1234567890123456789"
               export TZDATA_DIR="$PWD/tzdata"
             '';
+            enterTest = ''
+              mix test
+            '';
             processes.mqtt = {
               exec =
                 "${pkgs.mosquitto}/bin/mosquitto -p ${toString mosquitto_port}";
             };
+            process.process-compose = {
+              port = process_compose_port;
+              tui = true;
+            };
             services.postgres = {
               enable = true;
               package = pkgs.postgresql_15;
@@ -148,6 +151,13 @@
               '';
             };
           }];
+
         };
+      in {
+        packages = {
+          devenv-up = devShell.config.procfileScript;
+          default = pkg;
+        };
+        devShells.default = devShell;
       });
 }