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.

M1/Numerical Optimisation/ComputerSession3.ipynb

@@ -39,8 +39,8 @@
     }
    ],
    "source": [
-    "import numpy as np\n",
     "import matplotlib.pyplot as plt\n",
+    "import numpy as np\n",
     "\n",
     "\n",
     "def generate_thetas(n):\n",
@@ -211,9 +211,9 @@
     }
    ],
    "source": [
+    "import matplotlib.pyplot as plt\n",
     "import numpy as np\n",
     "from scipy.optimize import minimize\n",
-    "import matplotlib.pyplot as plt\n",
     "\n",
     "\n",
     "def polygon_perimeter(theta, n):\n",