fix: skip jax tests when jax is not installed

Add pytest.importorskip("jax") at module level in both test_jax_init.py
and test_jax_init_integration.py so CI environments without jax skip
these tests instead of failing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: rjpower

lib/iris/tests/test_jax_init.py

@@ -8,6 +8,8 @@
 
 import pytest
 
+pytest.importorskip("jax")
+
 from iris.actor.resolver import ResolveResult, ResolvedEndpoint
 from iris.cluster.client.job_info import JobInfo
 from iris.cluster.types import JobName

lib/iris/tests/test_jax_init_integration.py

@@ -25,6 +25,8 @@
 
 import pytest
 
+pytest.importorskip("jax")
+
 from iris.actor.resolver import ResolveResult, ResolvedEndpoint
 from iris.cluster.client.job_info import JobInfo
 from iris.cluster.types import JobName