feat: 添加Mistral渠道 (close #546)

common/constants.go

@@ -222,6 +222,7 @@ const (
 	ChannelCloudflare         = 39
 	ChannelTypeSiliconFlow    = 40
 	ChannelTypeVertexAi       = 41
+	ChannelTypeMistral        = 42
 
 	ChannelTypeDummy // this one is only for count, do not add any channel after this
 
@@ -270,4 +271,5 @@ var ChannelBaseURLs = []string{
 	"https://api.cloudflare.com",                //39
 	"https://api.siliconflow.cn",                //40
 	"",                                          //41
+	"https://api.mistral.ai",                    //42
 }