fix(adk-middleware): map oneOf → anyOf so genai keeps discriminated-union tool params

[jplikesbikes]

Fix: map oneOf → anyOf in ADK middleware schema cleaner

Problem

google.genai's types.Schema accepts anyOf but not oneOf. The ADK middleware's _clean_schema_for_genai filters tool-parameter schemas through an allowlist derived from types.Schema.model_fields, so any oneOf key was silently dropped.

This erases the structure of discriminated unions. CopilotKit / AG-UI frontend tools serialize a zod discriminatedUnion to oneOf (via zod-to-json-schema), so any frontend tool with such a parameter reached Gemini as a bare {description} object with no fields — and the model would just invent a shape.

Fix

Map oneOf → anyOf recursively (cleaning each branch), alongside the existing examples → example and const → enum mappings. For tool-argument schemas the oneOf/anyOf distinction is immaterial: the model emits exactly one branch either way.

This mirrors prior Gemini-compat fixes — #1919 (additionalProperties) and #1664 (nested required).

Changes

• client_proxy_tool.py: add the oneOf → anyOf mapping in _clean_schema_for_genai.
• test_client_proxy_tool.py: add tests covering a flat oneOf mapping and a nested discriminated-union schema where each branch is recursively cleaned ($-keys / rejected keys stripped, const → enum) and the sibling description is preserved.

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[jplikesbikes]

@contextablemark Just wanted to bring this to your attention no rush

[jplikesbikes]

@contextablemark friendly reminder