🚚 Refactor(ratio_setting): refactor ratio management into standalone ratio_setting package

Summary
• Migrated all ratio-related sources into `setting/ratio_setting/`
  – `model_ratio.go` (renamed from model-ratio.go)
  – `cache_ratio.go`
  – `group_ratio.go`
• Changed package name to `ratio_setting` and relocated initialization (`ratio_setting.InitRatioSettings()` in main).
• Updated every import & call site:
  – Model / cache / completion / image ratio helpers
  – Group ratio helpers (`GetGroupRatio*`, `ContainsGroupRatio`, `CheckGroupRatio`, etc.)
  – JSON-serialization & update helpers (`*Ratio2JSONString`, `Update*RatioByJSONString`)
• Adjusted controllers, middleware, relay helpers, services and models to reference the new package.
• Removed obsolete `setting` / `operation_setting` imports; added missing `ratio_setting` imports.
• Adopted idiomatic map iteration (`for key := range m`) where value is unused.
• Ran static checks to ensure clean build.

This commit centralises all ratio configuration (model, cache and group) in one cohesive module, simplifying future maintenance and improving code clarity.

main.go

@@ -12,7 +12,7 @@ import (
 	"one-api/model"
 	"one-api/router"
 	"one-api/service"
-	"one-api/setting/operation_setting"
+	"one-api/setting/ratio_setting"
 	"os"
 	"strconv"
 
@@ -74,7 +74,7 @@ func main() {
 	}
 
 	// Initialize model settings
-	operation_setting.InitRatioSettings()
+	ratio_setting.InitRatioSettings()
 	// Initialize constants
 	constant.InitEnv()
 	// Initialize options