python312Packages.scipy: Allow building with Numpy 1

pkgs/development/python-modules/scipy/default.nix

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       excludes = [ "doc/source/dev/contributor/meson_advanced.rst" ];
     })
   ];
+  # A NOTE regarding the Numpy version relaxing: Both Numpy versions 1.x &
+  # 2.x are supported. However upstream wants to always build with Numpy 2,
+  # and with it to still be able to run with a Numpy 1 or 2. We insist to
+  # perform this substitution even though python3.pkgs.numpy is of version 2
+  # nowadays, because our ecosystem unfortunately doesn't allow easily
+  # separating runtime and build-system dependencies. See also:
+  #
+  # https://discourse.nixos.org/t/several-comments-about-priorities-and-new-policies-in-the-python-ecosystem/51790
+  #
+  # Being able to build (& run) with Numpy 1 helps for python environments
+  # that override globally the `numpy` attribute to point to `numpy_1`.
+  postPatch = ''
+    substituteInPlace pyproject.toml \
+      --replace-fail "numpy>2.0.0,<2.5" numpy
+  '';
 
   build-system =
     [