feat(ai): add native DeepInfra provider

[rekram1-node]

Issue for this PR

N/A

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Adds a first-class DeepInfra provider using the existing OpenAI Chat protocol without changing the shared protocol. Core maps the DeepInfra SDK identifier to the native provider, preserves API roots and authentication, and removes the obsolete SDK dependency and provider plugin. Includes recorded text, tool-call, and tool-loop fixtures.

How did you verify your code works?

• DeepInfra recorded scenarios and native/OpenAI-compatible provider tests: 28 passed.
• Core provider mapping, model resolution, plugin factory, and provider-loading tests: 65 passed.
• Provider package entrypoint tests: 2 passed.
• AI, Core, Server, SDK, and CLI package typechecks: passed.
• Workerd bundle probe and frozen-lockfile install: passed.
• Confirmed recording fixtures contain no credentials or authentication headers.

Screenshots / recordings

N/A

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR