Resolve a provider specification into a full provider config.

Accepts:

• Atoms (e.g. :openai, :anthropic) — mapped to provider modules
• Maps with :adapter and :base_url — used as-is
• Modules implementing LLM.Provider behaviour
• Tuples {module, opts} — module with runtime options (e.g., api_key)

Examples

LLM.Provider.Resolver.resolve(:openai)
#=> %{adapter: LLM.Adapter.OpenAI, base_url: "https://api.openai.com/v1", ...}

LLM.Provider.Resolver.resolve(LLM.Provider.Anthropic)
#=> %{adapter: LLM.Adapter.Anthropic, base_url: "https://api.anthropic.com", ...}

LLM.Provider.Resolver.resolve({LLM.Provider.OpenAI, api_key: "sk-..."})
#=> %{adapter: LLM.Adapter.OpenAI, base_url: "https://api.openai.com/v1", api_key: "sk-..."}

LLM.Provider.Resolver.resolve(%{
  adapter: LLM.Adapter.OpenAI,
  base_url: "http://localhost:11434/v1"
})
#=> %{adapter: LLM.Adapter.OpenAI, base_url: "http://localhost:11434/v1", api_key: nil}