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.

M2/Machine Learning/TP_1/2025_TP_1_M2_ISF.ipynb

@@ -226,7 +226,7 @@
    "source": [
     "print(range(4, 10))\n",
     "print(range(5, 50, 3))\n",
-    "print([3, 1, 4] + [1, 5, 9])\n",
+    "print([3, 1, 4, 1, 5, 9])\n",
     "print(len(range(4, 10)))"
    ]
   },
@@ -282,7 +282,7 @@
     "\n",
     "print(num in [1, 2, 3] and num > 0)\n",
     "\n",
-    "print(not 5 == 3)"
+    "print(5 != 3)"
    ]
   },
   {