fix metadata parsing exception in document_store.py

[salvogs]

Bug Report: JMESPath Filter Parse Error with Escaped Single Quotes

Problem Description
The _get_jmespath_filter function in [document_store.py] causes a parsing error when processing metadata filters that contain single quotes. The function incorrectly escapes single quotes by adding backslashes, which creates invalid JMESPath syntax.

Error Message:

pathway.engine.EngineError: Parse error: Invalid character: \ (line 0, column 11)
(category=='food')

Root Cause:

In line 38 of [document_store.py], the function performs this transformation:

metadata_filter.replace("'", r"\'").replace("`", "'").replace('"', "")

When a metadata filter like category=='food' is processed, it becomes category=='food', which contains escaped single quotes that are invalid in JMESPath syntax.

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[szymondudycz]

Hey @salvogs, thanks for this pull request - after looking at this issue I agree that this needs to be fixed. I think, however, that you should completely remove the whole line. More importantly, currently our tests are incorrect and would fail after your change (in python/pathway/xpack/llm/tests), so these would need to be fixed. Finally, this change would require an entry in the changelog, marking this change as breaking.