[BUG] @validate_callback decorator applied at class level doesn't validate overridden methods in subclasses

[Tushar8466]

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Describe the Bug

In pygam/callbacks.py, the @validate_callback decorator is applied directly
on the class definitions at module load time:

@validate_callback
class Deviance(CallBack):
    ...

Inside validate_callback, the wrapping is done using setattr on
on_loop_start / on_loop_end methods once, when the file is first
imported. This means if a user subclasses Deviance (or any other callback)
and overrides on_loop_start or on_loop_end, the new method will not
be wrapped by validate_callback_data.

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Steps to Reproduce

from pygam.callbacks import Deviance, validate_callback_data

class MyCallback(Deviance):
    def on_loop_start(self, gam, y, mu, some_invalid_arg):
        return 42  # This override is never validated

cb = MyCallback()
# No error is raised, even though the method signature is wrong
# The validation was only applied to Deviance, not MyCallback

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Expected Behavior

Subclasses that override on_loop_start or on_loop_end should either:

• Be automatically re-validated when instantiated, or
• Raise a clear error if their method signature references arguments
  not available in the callback data vars dict

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Actual Behavior

No validation occurs on overridden methods in subclasses. The bug can
silently pass through and only fail at runtime during model fitting,
with a confusing error message unrelated to the real cause.

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Root Cause

validate_callback uses setattr to wrap methods on the instance or
class passed to it. Since @validate_callback is applied at class
definition time, it only wraps the methods of the decorated class —
not any future subclasses.

# This only wraps Deviance.on_loop_start once at import time
@validate_callback
class Deviance(CallBack):
    ...

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Suggested Fix

Move validation to __init_subclass__ or to the CallBack base class
__init__ method, so that every new subclass or instance is validated
at creation time:

class CallBack(Core):
    def __init__(self, name=None):
        super().__init__(name=name)
        validate_callback(self)  # validate at instance creation

This ensures all subclasses — including user-defined ones — are validated
regardless of when or how they are created.

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Environment

Detail	Info
File	pygam/callbacks.py
Affected Classes	Deviance, Accuracy, Diffs, Coef and any user-defined subclasses
Decorator	@validate_callback
Impact	All versions using the current decorator pattern

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Labels

bug callbacks subclassing validation

[Tushar8466]

@dswah I would like to work on this issue . Please assign me this issue

[Tushar8466]

#574 This PR resolves this issue