Configuration for file search capabilities in threads and runs.
File search allows agents to search through uploaded files using vector stores.
@type t() :: %Codex.FileSearch{ filters: map() | nil, include_search_results: boolean() | nil, ranking_options: map() | nil, vector_store_ids: [String.t()] | nil }
@spec merge(t() | nil, t() | nil) :: t() | nil
@spec new(map() | keyword() | t() | nil) :: {:ok, t() | nil} | {:error, term()}