feat: Add Anthropic Messages API support (#7948)

* Initial plan

* Add Anthropic Messages API support

Co-authored-by: mudler <2420543+mudler@users.noreply.github.com>

* Fix code review comments: add error handling for JSON operations

Co-authored-by: mudler <2420543+mudler@users.noreply.github.com>

* Fix test suite to use existing schema test runner

Co-authored-by: mudler <2420543+mudler@users.noreply.github.com>

* Add Anthropic e2e tests using anthropic-sdk-go for streaming and non-streaming

Co-authored-by: mudler <2420543+mudler@users.noreply.github.com>

* Co-authored-by: mudler <2420543+mudler@users.noreply.github.com>

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: mudler <2420543+mudler@users.noreply.github.com>