Explicitly require NumPy 1.21+

As NumPy is used internally, list it as an explicit requirement instead
of relying on other dependencies to pull it in.

conda/recipes/cuxfilter/meta.yaml

@@ -35,6 +35,7 @@ requirements:
  - libwebp
  - nodejs >=14
  - numba >=0.57
+ - numba >=1.21
  - packaging
  - panel >=0.14.0,<=0.14.1
  - pydeck >=0.3,<=0.5.0