[ES|QL] Change rounding mode in tests to HALF_DOWN (elastic#129895) (elastic#129899)

The current rounding mode in some of the tests in ESQL uses DOWN which
truncates more than rounds and can result in some tests failing with
errors like `row 0 column 0:0: expected <0.05235999> but was <0.05236>`
HALF_DOWN would round this up

Author: limotova

x-pack/plugin/esql/qa/server/src/main/java/org/elasticsearch/xpack/esql/qa/rest/EsqlSpecTestCase.java

@@ -350,9 +350,9 @@ private Object valueMapper(CsvTestUtils.Type type, Object value) {
                 }
                 return values;
             } else if (value instanceof Double d) {
-                return new BigDecimal(d).round(new MathContext(7, RoundingMode.DOWN)).doubleValue();
+                return new BigDecimal(d).round(new MathContext(7, RoundingMode.HALF_DOWN)).doubleValue();
             } else if (value instanceof String s) {
-                return new BigDecimal(s).round(new MathContext(7, RoundingMode.DOWN)).doubleValue();
+                return new BigDecimal(s).round(new MathContext(7, RoundingMode.HALF_DOWN)).doubleValue();
             }
         }
         if (type == CsvTestUtils.Type.TEXT || type == CsvTestUtils.Type.KEYWORD || type == CsvTestUtils.Type.SEMANTIC_TEXT) {