test(core): simplify provider smoke tests

[kitlangton]

Why
Several provider registration checks were synchronous assertions wrapped in the full Effect plugin harness. Nearby provider suites also retained unused service acquisitions, same-instance provisioning, nested service reads, or import aliases that did not contribute to their scenarios.

What Changes

• Registers the Kilo, LLMGateway, NVIDIA, OpenRouter, Zenmux, and LM Studio catalog-membership assertions as ordinary Bun tests.
• Keeps hook, catalog, integration, discovery, and local-server behavior cases on the existing Effect harness.
• Removes dead Plugin/AISDK acquisitions from Dynamic, Vercel, and GitHub Copilot cases.
• Calls LLMGateway and OpenAI plugins with their ambient Integration services instead of fetching and re-providing the same instance.
• Binds GitHub Copilot and OpenAI Integration/PluginHooks services before invoking their methods.
• Uses convertToOpenAICompatibleChatMessages directly throughout its converter suite.

Scope
This changes test setup only. Provider registration contents, plugin behavior, local discovery, historical compatibility assertions, and converter expectations are unchanged. OpenAI catalog behavior remains owned by #45336, GitHub Copilot title behavior by #43794, and LM Studio reasoning behavior by #43076.

Verification

cd packages/core
bun run test test/plugin/provider-kilo.test.ts test/plugin/provider-llmgateway.test.ts test/plugin/provider-nvidia.test.ts test/plugin/provider-openrouter.test.ts test/plugin/provider-zenmux.test.ts test/plugin/provider-vercel.test.ts test/plugin/provider-dynamic.test.ts test/github-copilot/convert-to-copilot-messages.test.ts
bun run test test/plugin/provider-lmstudio.test.ts test/plugin/provider-github-copilot.test.ts test/plugin/provider-openai.test.ts
bun typecheck

cd ../..
bun turbo typecheck --concurrency=3
bun prettier --check packages/core/test/plugin/provider-kilo.test.ts packages/core/test/plugin/provider-llmgateway.test.ts packages/core/test/plugin/provider-nvidia.test.ts packages/core/test/plugin/provider-openrouter.test.ts packages/core/test/plugin/provider-zenmux.test.ts packages/core/test/plugin/provider-vercel.test.ts packages/core/test/plugin/provider-dynamic.test.ts packages/core/test/github-copilot/convert-to-copilot-messages.test.ts packages/core/test/plugin/provider-lmstudio.test.ts packages/core/test/plugin/provider-github-copilot.test.ts packages/core/test/plugin/provider-openai.test.ts
git diff --check origin/v2...HEAD

50 original focused tests and 27 continuation tests passed. Core and push-hook workspace typechecks passed. Formatting and diff checks passed; scoped lint reported zero errors with pre-existing fixture assertion warnings only.