In MariaDB, `long_query_time`[1] and `max_statement_time`[2] have up to
microsecond granularity (6 digits to the right of the decimal).
Fixes an issue detected by proxysql in staging.
```
MySQL_Session.cpp:6567:handler___status_WAITING_CLIENT_DATA___STATE_SLEEP___MYSQL_COM_QUERY_qpo(): [ERROR] Unable to parse query. If correct, report it as a bug: SET long_query_time=3.9200000000000004
```
1. https://mariadb.com/kb/en/server-system-variables/#long_query_time
2. https://mariadb.com/kb/en/server-system-variables/#max_statement_time
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Co-authored-by: Aaron Gable <aaron@letsencrypt.org>
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