LCORE-3315: Adapt to new OGX OpenApi client

[asimurka]

Description

This PR adapts Lightspeed Core to the new OGX OpenAPI client surface: call sites and tests move off the old client APIs (for example model listing via openai.list(), service-client headers via api_client, and rebuilding clients where .copy() is gone), Azure/provider-data handling is centralized in a shared read_provider_data helper reused by the Pydantic AI provider, and the Singleton metaclass typing is tightened without changing runtime behavior.

Type of change

• Refactor
• New feature
• Bug fix
• CVE fix
• Optimization
• Documentation Update
• Configuration Update
• Bump-up service version
• Bump-up dependent library [pyproject.toml + uv.lock]
• Bump-up dependent library [requirements.*.txt for Konflux]
• Bump-up library or tool used for development (does not change the final image)
• CI configuration change
• Konflux configuration change
• Unit tests improvement
• Integration tests improvement
• End to end tests improvement
• Benchmarks improvement

Tools used to create PR

Identify any AI code assistants used in this PR (for transparency and review context)

• Assisted-by: Cursor

Related Tickets & Documents

• Related Issue #
• Closes # https://redhat.atlassian.net/browse/LCORE-3315

Checklist before requesting a review

• I have performed a self-review of my code.
• PR has passed all pre-merge test jobs.
• If it is a core feature, I have added thorough tests.

Testing

• Please provide detailed steps to perform tests related to this code change.
• How were the fix/results from this change verified? Please provide relevant screenshots or results.

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[asimurka]

With this adjustment, typechecker can correctly infer underlying type of singleton object.