Configures Python environment for project

Adds a `.env` file to define the `PYTHONPATH` variable, ensuring
module resolution from the `src` directory. Configures VS Code
settings to use the `.env` file and enhance Python analysis
with extra paths.

Improves development environment setup.

.env

@@ -0,0 +1 @@
+PYTHONPATH=src

.vscode/settings.json

@@ -0,0 +1,6 @@
+{
+    "python.envFile": "${workspaceFolder}/.env",
+    "python.analysis.extraPaths": [
+        "src"
+    ]
+}