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/resolver.go

@@ -47,6 +47,19 @@ func Token2FutureSymbols(token string) []string {
 }
 
 func Token2SpotSymbols(token string) []string {
+	if !stringx.IsAlphaNumeric(token) {
+		return nil
+	}
+
+	spotOnly := strings.ToUpper(token) + "USDT"
+	if data.Market.IsSpotPair(spotOnly) {
+		return []string{spotOnly}
+	}
+
+	return nil
+}
+
+func Token2RelatedSpotSymbols(token string) []string {
 	futureSymbols := Token2FutureSymbols(token)
 	spots := make([]string, 0, len(futureSymbols)+1)
 	seen := make(map[string]struct{}, len(futureSymbols)+1)