Reduce numpy lower bound back to 1.21.2

Author: ValerianRey

pyproject.toml

@@ -15,7 +15,7 @@ requires-python = ">=3.10"
 dependencies = [
     "torch>=2.4.0",  # Problems before 2.4.0, especially with autogram.
     "quadprog>=0.1.9, != 0.1.10",  # Doesn't work before 0.1.9, 0.1.10 is yanked
-    "numpy>=1.23.0",  # Does not work before 1.21. No python 3.10 wheel before 1.21.2. matplotlib (required for lightning) requires numpy >= 1.23.0.
+    "numpy>=1.21.2",  # Does not work before 1.21. No python 3.10 wheel before 1.21.2.
     "qpsolvers>=1.0.1",  # Does not work before 1.0.1
 ]
 classifiers = [
@@ -95,7 +95,7 @@ plot = [
 # Dependency group allowing to easily resolve version of the core dependencies to the lower bound.
 lower_bounds = [
     "torch==2.4.0",
-    "numpy==1.23.0",
+    "numpy==1.21.2",
     "quadprog==0.1.9",
     "qpsolvers==1.0.1",
 ]