Change series field type from :msg to :text

Update example to use :text for string fields in series. This aligns
with the new :text type support in the series implementation.

examples/soa_series.myc

@@ -2,7 +2,7 @@
 ;; Benchmark: 1.0us
 ;; Benchmark-Repeat: 1944
 (do
-  (def my_ticks (series {:price :float :volume :int :msg :string}))
+  (def my_ticks (series {:price :float :volume :int :msg :text}))
 
   (push my_ticks {:price 10.5 :volume 100 :msg "A"})
   (push my_ticks {:price 11.2 :volume 200 :msg "B"})