@spec build_client(TruelayerClient.Config.t()) :: Req.Request.t()

Build a Req.Request base client from a TruelayerClient.Config.

@spec form_post(Req.Request.t(), String.t(), map()) ::
  {:ok, map()} | {:error, TruelayerClient.Error.t()}

Execute an application/x-www-form-urlencoded POST request.

Used exclusively for OAuth2 token-endpoint calls.

@spec json_request(Req.Request.t(), TruelayerClient.Config.t(), keyword()) ::
  {:ok, term()} | {:error, TruelayerClient.Error.t()}

Execute a JSON request.

Returns {:ok, decoded_body} for 2xx responses or {:error, %TruelayerClient.Error{}} for errors.