chore(di): cache function code pair resolution (#11757)

We make sure to cache the result of the function code pair resolution
for subsequent calls.

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## Reviewer Checklist
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Author: P403n1x87

ddtrace/debugging/_function/discovery.py

@@ -159,7 +159,8 @@ def resolve(self) -> FullyNamedFunction:
             msg = f"Multiple functions found for code object {code}"
             raise ValueError(msg)
 
-        f = cast(FullyNamedFunction, functions[0])
+        self.function = _f = functions[0]
+        f = cast(FullyNamedFunction, _f)
         f.__fullname__ = f"{f.__module__}.{f.__qualname__}"
 
         return f
@@ -254,15 +255,17 @@ def __init__(self, module: ModuleType) -> None:
         if hasattr(module, "__dd_code__"):
             for code in module.__dd_code__:
                 fcp = _FunctionCodePair(code=code)
+
                 if PYTHON_VERSION_INFO >= (3, 11):
                     # From this version of Python we can derive the qualified
                     # name of the function directly from the code object.
                     fullname = f"{module.__name__}.{code.co_qualname}"
                     self._fullname_index[fullname] = fcp
                 else:
                     self._name_index[code.co_name].append(fcp)
+
                 for lineno in linenos(code):
-                    self[lineno].append(_FunctionCodePair(code=code))
+                    self[lineno].append(fcp)
         else:
             # If the module was already loaded we don't have its code object
             seen_functions = set()