Langchain Integration: broken on Optimizer

[dat-boris]

Hi there,

Following the notebook at https://github.com/stanfordnlp/dspy/blob/main/examples/tweets/compiling_langchain.ipynb

• Running this in the latest release (2.4.9) will cause this issue Langchain Integration Broken on Change in dspy.signatures.field  #887 (AttributeError: 'FieldInfo' object has no attribute 'finalize'")
• Thankfully there's already a patch! 🎉 After applying the fix at Langchain integration bug fixed #1015, it will continue to run but then show the following error on optimizer.compile:

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Cell In[11], line 6
      3 optimizer = BootstrapFewShotWithRandomSearch(metric=metric, max_bootstrapped_demos=3, num_candidate_programs=3)
      5 # Now use the optimizer to *compile* the chain. This could take 5-10 minutes, unless it's cached.
----> 6 optimized_chain = optimizer.compile(zeroshot_chain, trainset=trainset, valset=valset)

File ~/dspy/teleprompt/random_search.py:96, in BootstrapFewShotWithRandomSearch.compile(self, student, teacher, trainset, valset, restrict, labeled_sample)
     86 elif seed == -1:
     87     # unshuffled few-shot
     88     program = BootstrapFewShot(
     89         metric=self.metric,
     90         metric_threshold=self.metric_threshold,
   (...)
     94         max_rounds=self.max_rounds,
     95     )
---> 96     program2 = program.compile(student, teacher=teacher, trainset=trainset2)
     98 else:
     99     assert seed >= 0, seed

File ~/dspy/teleprompt/bootstrap.py:83, in BootstrapFewShot.compile(self, student, teacher, trainset)
     80 self.trainset = trainset
     82 self._prepare_student_and_teacher(student, teacher)
---> 83 self._prepare_predictor_mappings()
     84 self._bootstrap()
     86 self.student = self._train()

File ~/dspy/teleprompt/bootstrap.py:115, in BootstrapFewShot._prepare_predictor_mappings(self)
    113 for (name1, predictor1), (name2, predictor2) in zip(student.named_predictors(), teacher.named_predictors()):
    114     assert name1 == name2, "Student and teacher must have the same program structure."
--> 115     assert predictor1.signature.equals(
    116         predictor2.signature,
    117     ), (f"Student and teacher must have the same signatures. "
    118         f"{type(predictor1.signature)} != {type(predictor2.signature)}"
    119         )
    120     assert id(predictor1) != id(predictor2), "Student and teacher must be different objects."
    122     name2predictor[name1] = None  # dict(student=predictor1, teacher=predictor2)

AttributeError: 'Template' object has no attribute 'equals'

Seems like optimizer was expecting equals method (maybe with dspy.Signature?) - it is not there for type of dsp.template_v3.Template.

Related to upgrade potentially at #451