feat: Expose __ffi_init__ as a de-facto shortcut to calling _C___init__

[junrushao]

Per discussion w/ @tqchen.

In dataclass-syntax classes as introduced in #8, we likely always use the reflected _C___init__ method to initialize an instance. This PR gives a shortcut to this convention, where

self.__init_handle_by_constructor__(_MyClass._C___init__, ...)

is equivalent to

self.__ffi_init__(v_i64 + 1, v_i32 + 2)

[Copilot]

Pull Request Overview

Adds a convenience initializer method to mirror calling the reflected C++ _C___init__ constructor and exposes an additional field on TypeField.

• Introduces Object.ffi_init as a shortcut to init_handle_by_constructor(type(self).C___init_, ...).
• Updates type stubs accordingly and adds a new dataclass_field attribute to TypeField.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
python/tvm_ffi/cython/object.pxi	Adds ffi_init convenience wrapper with docstring.
python/tvm_ffi/core.pyi	Adds stub for ffi_init and new TypeField.dataclass_field attribute.

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[Copilot]

[nitpick] Same docstring issues as implementation: backticked name contains an extra space ( __init__) and parameter description should reflect variadic positional arguments rather than 'list of objects'. Mirror the corrected wording in the implementation for consistency.

Suggested change

	"""Initialize the instance using the ` __init__` method registered on C++ side.
	Parameters
	----------
	args: list of objects
	The arguments to the constructor
	"""Initialize the instance using the `__init__` method registered on the C++ side.
	Parameters
	----------
	args
	Positional arguments to pass to the constructor.

[Copilot]

[nitpick] New attribute dataclass_field is added without any doc/comment explaining its purpose or when it may be None. Consider adding a brief class-level note or inline comment to clarify its role (e.g., link to dataclass reflection mechanism) to aid future maintainability.

Suggested change

	setter: Any
	setter: Any
	# Reference to the corresponding dataclass field, if the FFI-backed type is also a Python dataclass.
	# May be None if no dataclass field is associated (e.g., for non-dataclass types).

[tqchen]

minor nit, on c function naming, how about __c_init__ for the pattern, it aligns with other dlpack style dunder naming(see dmlc/dlpack#175, also shorter to type in def_static

[junrushao]

Merged this PR into #8