Fix integer overflow (#435)

* Fix MAX_BUCKETS_MEM overflow

* Fix MAX_QUERY_BUF overflow

* Fix int overflow in IsBucketValid function

* Add missing newline

* Remove test for max value of pgsm_query_shared_buffer parameter

* Tune tests

* Cleanup

* Use int64 type instead of long long

t/expected/031_query_stat.out

@@ -0,0 +1,21 @@
+CREATE EXTENSION pg_stat_monitor;
+SELECT pg_stat_monitor_reset();
+ pg_stat_monitor_reset 
+-----------------------
+ 
+(1 row)
+
+SELECT 1 AS num;
+ num 
+-----
+   1
+(1 row)
+
+SELECT query, comments FROM pg_stat_monitor ORDER BY query COLLATE "C";
+             query              | comments 
+--------------------------------+----------
+ SELECT 1 AS num                | 
+ SELECT pg_stat_monitor_reset() | 
+(2 rows)
+
+DROP EXTENSION pg_stat_monitor;