[v11.0.x] MySQL: snapshot tests (#86184)

MySQL: snapshot tests (#84846)

mysql: add snapshot tests
(cherry picked from commit 3b7ee3a56b)

Co-authored-by: Gábor Farkas <gabor.farkas@gmail.com>

pkg/tsdb/mysql/testdata/table/timestamp_convert_float.sql

@@ -0,0 +1,15 @@
+-- SELECT * FROM tbl
+-- the time-field and time-end field gets converted to time.Time
+CREATE TABLE tbl (
+    -- note, in the timestmap below we must say `NULL` otherwise mysql-below-8 inserts current timestamp
+    reallyt timestamp(6) NULL, -- reference real timestamp
+    "time" real,
+    n real, -- normal number, it should not get converted to a timestamp
+    timeend bigint
+);
+
+INSERT INTO tbl (reallyt, "time", n, timeend) VALUES
+('2023-12-21T12:22:24', 1703161344, 1703161344, 1703161372),
+('2023-12-21T12:20:33.408', 1703161233408, 1703161233408, 1703161312522),
+('2023-12-21T12:20:41.050022', 1703161241050021888, 1703161241050021888, 1703161312522186000),
+(NULL, NULL, NULL, NULL);