Refactor code in numerical methods notebooks

- Updated import order in Point_Fixe.ipynb for consistency.
- Changed lambda functions to regular function definitions for clarity in Point_Fixe.ipynb.
- Added numpy import in TP1_EDO_EulerExp.ipynb, TP2_Lokta_Volterra.ipynb, and TP3_Convergence.ipynb for better readability.
- Modified for loops in TP1_EDO_EulerExp.ipynb and TP2_Lokta_Volterra.ipynb to include strict=False for compatibility with future Python versions.

L3/Equations Différentielles/TP2_Lokta_Volterra.ipynb

@@ -92,14 +92,14 @@
    ],
    "source": [
     "%matplotlib inline\n",
-    "import numpy as np\n",
     "import matplotlib.pyplot as plt\n",
+    "import numpy as np\n",
     "\n",
     "\n",
     "# Fonction F définissant l'EDO\n",
     "def F(Y):\n",
-    "    x = Y[0]\n",
-    "    y = Y[1]\n",
+    "    Y[0]\n",
+    "    Y[1]\n",
     "    A = np.array([[0, 1], [-2, -3]])\n",
     "    return np.dot(A, Y)\n",
     "\n",
@@ -132,7 +132,7 @@
     "## Représentation des solutions pour chaque valeur de la donnée initiale\n",
     "tt = np.linspace(-10, 10, 100)\n",
     "t0 = tt[0]\n",
-    "for x, y in zip([1, -2, 0, 1, 3], [2, -2, -4, -2, 4]):\n",
+    "for x, y in zip([1, -2, 0, 1, 3], [2, -2, -4, -2, 4], strict=False):\n",
     "    sol = uex(tt, t0, [x, y])\n",
     "    plt.plot(sol[0], sol[1], label=f\"$((x0, y0) = ({x}, {y})$\")\n",
     "    plt.scatter(x, y)\n",