chore(tracer): add metastruct data to span repr for debug logs (#16278)

## Description

Add metastruct data to span repr for debug logs.
Each value must be a dictionary. Add the list of keys of each value or
an error string if it's not a dict

## Testing

Add unit test

APPSEC-61027

Author: christophe-papazian

ddtrace/_trace/span.py

@@ -782,6 +782,10 @@ def __exit__(
 
     def __repr__(self) -> str:
         """Return a detailed string representation of a span."""
+        meta = {
+            k: v.keys() if isinstance(v, dict) else f"wrong type [{type(v).__name__}]"
+            for k, v in self._meta_struct.items()
+        }
         return (
             f"Span(name='{self.name}', "
             f"span_id={self.span_id}, "
@@ -799,7 +803,8 @@ def __repr__(self) -> str:
             f"links={self._links}, "
             f"events={self._events}, "
             f"context={self.context}, "
-            f"service_entry_span_name={self._service_entry_span.name})"
+            f"service_entry_span_name={self._service_entry_span.name}), "
+            f"metastruct={meta}"
         )
 
     def __str__(self) -> str:

tests/tracer/test_span.py

@@ -987,3 +987,11 @@ def deep_error(n):
     split_result = [s + "\n" for item in split_result for s in item.split("\n") if s]
     assert len(split_result) < 8  # Value is 5 for Python 3.10
     assert len(result) < 410  # Value is 377 for Python 3.10
+
+
+def test_span_repr_metastruct():
+    span = Span("span_test")
+    assert "metastruct={}" in repr(span)
+    span._set_struct_tag("key1", {"a": 1, "b": 2})
+    span._set_struct_tag("key2", ["bad item"])  # type: ignore
+    assert "metastruct={'key1': dict_keys(['a', 'b']), 'key2': 'wrong type [list]'}" in repr(span)