Updated toy data tutorial to use mrCOSTS module

- Toy data tutorial explanatory text cleaned up.
- Toy data plots corrected (wrong data were plotted in the first
  reconstruction plot).
- Toy data tutorial includes mrCOSTS fit demonstration.
- Changed to the hopefully correct kernel for the tutorial tests.

Author: klapo

tutorials/tutorial20/costs-tutorial_real-data.ipynb

@@ -2161,9 +2161,9 @@
  ],
  "metadata": {
   "kernelspec": {
-   "display_name": "Python [conda env:pydmd-mrd]",
+   "display_name": "Python 3 (ipykernel)",
    "language": "python",
-   "name": "conda-env-pydmd-mrd-py"
+   "name": "python3"
   },
   "language_info": {
    "codemirror_mode": {
@@ -2175,7 +2175,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.10.10"
+   "version": "3.10.13"
   }
  },
  "nbformat": 4,