ST_GEOHEX fix for excessive object creation in bounded grids (#130343)

Use new objects per thread instead of per record
* Expand tests to use random bounds, after multi-thread fix
* Also fix an issue around nulls for out-of-bounds results
* And investigate and affirm that the use of -1 internally to mark invalid grid-ids is fine for all three grid types (ie. -1 is not a valid grid-id in any of these cases, for different reasons in each).

Author: craigtaverner

x-pack/plugin/esql/src/main/generated/org/elasticsearch/xpack/esql/expression/function/scalar/spatial/StGeohashFromFieldAndLiteralAndLiteralEvaluator.java

@@ -17,20 +17,15 @@
 public class GeoHexBoundedPredicate {
 
     private final boolean crossesDateline;
-    private final GeoBoundingBox bbox;
+    private final GeoBoundingBox bbox, scratch;
 
     GeoHexBoundedPredicate(GeoBoundingBox bbox) {
         this.crossesDateline = bbox.right() < bbox.left();
-        // TODO remove this once we get serverless flaky tests to pass
-        // assert this.crossesDateline == false;
         this.bbox = bbox;
+        this.scratch = new GeoBoundingBox(new org.elasticsearch.common.geo.GeoPoint(), new org.elasticsearch.common.geo.GeoPoint());
     }
 
     public boolean validHex(long hex) {
-        GeoBoundingBox scratch = new GeoBoundingBox(
-            new org.elasticsearch.common.geo.GeoPoint(),
-            new org.elasticsearch.common.geo.GeoPoint()
-        );
         H3SphericalUtil.computeGeoBounds(hex, scratch);
         if (bbox.top() > scratch.bottom() && bbox.bottom() < scratch.top()) {
             if (scratch.left() > scratch.right()) {