build: promote jax_zero_contour to required dependency

Now the default critical_curves_method, so it must be installed on all
supported Python versions (including 3.13 CI which skips optional extras).

Author: Jammy2211

pyproject.toml

@@ -27,7 +27,8 @@ dependencies = [
     "autoarray",
     "colossus==1.3.1",
     "astropy>=5.0,<=7.2.0",
-    "nautilus-sampler==1.0.5"
+    "nautilus-sampler==1.0.5",
+    "jax_zero_contour"
 ]
 
 [project.urls]
@@ -47,7 +48,6 @@ local_scheme = "no-local-version"
 [project.optional-dependencies]
 optional=[
     "numba",
-    "jax_zero_contour",
     "pynufft",
     "ultranest==3.6.2",
     "zeus-mcmc==2.5.4",