Bug: partial variables not applied in ImagePromptTemplate.format()

[vladsfa]

Checked

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Feature request

Reproduction:

from langchain_core.prompts.image import ImagePromptTemplate

img = ImagePromptTemplate(
    input_variables=['img_data'],
    template={"url": "{img_data}", "detail": "high"}
).partial(img_data='test')

img.format()  # KeyError: 'img_data'

Expected Behavior:
The format() method should automatically merge partial_variables and return:
{"url": "test", "detail": "high"}

Actual Behavior:
It raises KeyError: 'img_data' because partial variables are not merged

Motivation

Bug fixing

Proposal (If applicable)

Add the following line at the beginning of langchain_core.prompts.image.ImagePromptTemplate.format:

kwargs = self._merge_partial_and_user_variables(**kwargs)