refactor: separate direct and related spot resolvers

Keep IsToken checks explicit across futures and direct spot symbols, move futures-derived spot mapping to a clearly named helper, and update token data collection to use related spot resolution.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

internal/helper/binancex/symbol.go

@@ -30,6 +30,9 @@ var (
 )
 
 func IsToken(s string) bool {
+	if len(Token2FutureSymbols(s)) > 0 {
+		return true
+	}
 	if len(Token2SpotSymbols(s)) > 0 {
 		return true
 	}