Pin Metatensor as tests broke with Metatrain release (#204)

* fix: pin metatensor because it is more unstable.

* fix: pin the dependencies for the metatensor tutorial

Author: CompRhys

examples/tutorials/metatensor_tutorial.py

@@ -3,8 +3,8 @@
 #   <summary>Dependencies</summary>
 # /// script
 # dependencies = [
-#     "metatrain[pet]>=2025.6",
-#     "metatensor-torch>=0.7,<0.8"
+#     "metatrain[pet]==2025.6",
+#     "metatensor-torch==0.7.6"
 # ]
 # ///
 # </details>

pyproject.toml

@@ -48,7 +48,7 @@ test = [
 io = ["ase>=3.24", "phonopy>=2.37.0", "pymatgen>=2024.11.3"]
 mace = ["mace-torch>=0.3.12"]
 mattersim = ["mattersim>=0.1.2"]
-metatensor = ["metatensor-torch>=0.7,<0.8", "metatrain[pet]>=2025.6"]
+metatensor = ["metatensor-torch==0.7.6", "metatrain[pet]==2025.6"]
 orb = ["orb-models>=0.5.2"]
 sevenn = ["sevenn>=0.11.0"]
 graphpes = ["graph-pes>=0.0.34", "mace-torch>=0.3.12"]