refactor(stream): remove dead type branches from getIntClaim (#5594)

The jwx library always deserializes numeric claims from a parsed token as
float64, so the int and int64 branches in getIntClaim could never succeed
and were dead code. Keep only the float64 path, which is the one actually
exercised by the token round-trip, and update the comment to document the
library behavior.

core/stream/token.go

@@ -92,17 +92,10 @@ func paramsFromToken(token jwt.Token) (*params, error) {
 	return &p, nil
 }
 
-// getIntClaim extracts an int claim from a JWT token, handling the case where
-// the value may be stored as int64 or float64 (common in JSON-based JWT libraries).
+// getIntClaim extracts a numeric claim from a JWT token. Numeric claims in a
+// parsed token are always deserialized as float64, regardless of the type used
+// when encoding.
 func getIntClaim(token jwt.Token, key string) int {
-	var v int
-	if err := token.Get(key, &v); err == nil {
-		return v
-	}
-	var v64 int64
-	if err := token.Get(key, &v64); err == nil {
-		return int(v64)
-	}
 	var f float64
 	if err := token.Get(key, &f); err == nil {
 		return int(f)