fix: Centralize OpenAPI schema reference resolution

[vblagoje]

Why:

Centralizes the OpenAPI schema reference resolution -> more simple and maintainable. Spec has references resolved at creation preventing subtle bugs (i.e parameters of an operationId not resolved properly).

What:

• Introduced jsonref loading and replacement within the OpenAPISpecification class constructor, ensuring all references are resolved upon object instantiation.

How can it be used:

• Not user facing

How did you test it:

• Ensured existing unit tests for the converter functions passed with the refactored codebase to verify backward compatibility and correctness.
• Adjusted test yaml service to include parameter reference

Notes for the reviewer:

• Pay special attention to how jsonref resolution was migrated to the OpenAPISpecification class constructor where instance variable spec_dict is by default reference resolved
• Review if the removal of jsonref_import.check() calls in converter functions could have any unintended side effects, although initial tests suggest the refactoring maintains the desired outcomes.

[coveralls]

Pull Request Test Coverage Report for Build 10028845050

Details

• 6 of 7 (85.71%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.02%) to 90.727%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
haystack_experimental/components/tools/openapi/_payload_extraction.py	1	2	50.0%

Totals
Change from base Build 9994763629:	-0.02%
Covered Lines:	1722
Relevant Lines:	1898

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💛 - Coveralls