feat: add environment variables and docs

ref: N25B-352

test/unit/test_get_config.py

@@ -0,0 +1,45 @@
+from robot_interface.utils.get_config import get_config
+
+
+def test_get_config_prefers_explicit_value(monkeypatch):
+    """
+    When a direct value is provided it should be returned without reading the environment.
+    """
+    monkeypatch.setenv("GET_CONFIG_TEST", "from-env")
+
+    result = get_config("explicit", "GET_CONFIG_TEST", "default")
+
+    assert result == "explicit"
+
+
+def test_get_config_returns_env_value(monkeypatch):
+    """
+    If value is None the environment variable should be used.
+    """
+    monkeypatch.setenv("GET_CONFIG_TEST", "from-env")
+
+    result = get_config(None, "GET_CONFIG_TEST", "default")
+
+    assert result == "from-env"
+
+
+def test_get_config_casts_env_value(monkeypatch):
+    """
+    The env value should be cast when a cast function is provided.
+    """
+    monkeypatch.setenv("GET_CONFIG_PORT", "1234")
+
+    result = get_config(None, "GET_CONFIG_PORT", 0, int)
+
+    assert result == 1234
+
+
+def test_get_config_casts_default_when_env_missing(monkeypatch):
+    """
+    When the env var is missing it should fall back to the default and still apply the cast.
+    """
+    monkeypatch.delenv("GET_CONFIG_MISSING", raising=False)
+
+    result = get_config(None, "GET_CONFIG_MISSING", "42", int)
+
+    assert result == 42