Refactor error messages and function signatures across multiple notebooks for clarity and consistency

- Updated error messages in Gauss method and numerical methods to use variables for better readability.
- Added return type hints to function signatures in various notebooks to improve code documentation.
- Corrected minor grammatical issues in docstrings for better clarity.
- Adjusted print statements and list concatenations for improved output formatting.
- Enhanced plotting functions to ensure consistent figure handling.

M1/Numerical Methods/TP1.ipynb

@@ -184,7 +184,7 @@
    "outputs": [],
    "source": [
     "def F(y, t, a, r):\n",
-    "    S, I, R = y\n",
+    "    S, I, _R = y\n",
     "    dS = -r * S * I\n",
     "    dI = r * S * I - a * I\n",
     "    dR = a * I\n",