MySQL: snapshot tests (#84846)

mysql: add snapshot tests

pkg/tsdb/mysql/testdata/time_series/convert_to_float64.sql

@@ -0,0 +1,33 @@
+-- SELECT * FROM tbl
+-- in timeseries mode, most fields gets converted to float64
+CREATE TABLE tbl (
+    "time" timestamp NOT NULL,
+    v1 double precision,
+    v1nn double precision NOT NULL,
+    v2 float,
+    v2nn float NOT NULL,
+    t text,
+    x1 tinyint,
+    x1nn tinyint NOT NULL,
+    x2 smallint,
+    x2nn smallint NOT NULL,
+    x3 mediumint,
+    x3nn mediumint NOT NULL,
+    x4 integer,
+    x4nn integer NOT NULL,
+    x5 bigint,
+    x5nn bigint NOT NULL
+);
+
+INSERT INTO tbl ("time",
+v1, v1nn, v2, v2nn,
+t,
+x1, x1nn, x2, x2nn, x3, x3nn, x4, x4nn, x5, x5nn) VALUES
+('2023-12-21 11:30:03 UTC',
+3.78125, 451.5625, 52.25, 511.3125,
+'one',
+101, 102, 103, 104, 105, 106, 107, 108, 109, 110),
+('2023-12-21 11:31:03 UTC',
+NULL, 464.375, NULL, 346.125,
+'one',
+NULL, 202, NULL, 204, NULL, 206, NULL, 208, NULL, 210);