This is the mirror image of #2170.

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Add `default_converter` argument to `to_js` and `toJs`. This is the mirror image of #2170.

### Checklists

<!-- Note on checklists:
     If you think some of these steps are not necessary for your PR,
     just remove those checkboxes, or mark them as checked. Otherwise,
     if some checkboxes are left unmarked, we might assume that your PR
     is not ready to be merged and we might keep you waiting -->

- [x] Add a [CHANGELOG](https://github.com/pyodide/pyodide/blob/main/docs/project/changelog.md) entry
- [x] Add / update tests
- [x] Add new / update outdated documentation

numpy.testing.decorators module has been removed from the new version of numpy. Add this back to be compatible with scipy.


diff --git a/numpy/testing/decorators.py b/numpy/testing/decorators.py
new file mode 100644
index 000000000..690a9a2c6
--- /dev/null
+++ b/numpy/testing/decorators.py
@@ -0,0 +1 @@
+from numpy.testing._private.decorators import *

numpy.testing.decorators module has been removed from the new version of numpy. Add this back to be compatible with scipy.


diff --git a/numpy/testing/decorators.py b/numpy/testing/decorators.py
new file mode 100644
index 000000000..690a9a2c6
--- /dev/null
+++ b/numpy/testing/decorators.py
@@ -0,0 +1 @@
+from numpy.testing._private.decorators import *
