include :: in name prefix check (#5951)

* include :: in name prefix check

```
import pymc as pm
with pm.Model("foo"):
    print(pm.Normal("foobar"), pm.Normal("baz"))
```

before: `foobar foo::baz`
after: `foo::foobar foo::baz`

* add a unit test

Author: moshelooks

pymc/model.py

@@ -1568,7 +1568,7 @@ def name_for(self, name):
         """Checks if name has prefix and adds if needed"""
         name = self._validate_name(name)
         if self.prefix:
-            if not name.startswith(self.prefix):
+            if not name.startswith(self.prefix + "::"):
                 return f"{self.prefix}::{name}"
             else:
                 return name

pymc/tests/test_model.py

@@ -159,6 +159,11 @@ def test_model_root(self):
             with pm.Model() as sub:
                 assert model is sub.root
 
+    def test_prefix_add_uses_separator(self):
+        with pm.Model("foo"):
+            foobar = pm.Normal("foobar")
+            assert foobar.name == "foo::foobar"
+
     def test_nested_named_model_repeated(self):
         with pm.Model("sub") as model:
             b = pm.Normal("var")