[ojuschugh1]

Fixes #16910

The problem was that ps_fetch_time() and ps_fetch_datetime() only print second_part when decimals is 1 to 6, the check added for bug #76386. MariaDB reports AUTO_SEC_PART_DIGITS (39) when the precision isn't known up front, for example for FROM_UNIXTIME('1992.1'), so prepared statements dropped the fraction that the text protocol returns.

I made any decimals above 6, the not-fixed sentinel (39 in MariaDB, 31 in MySQL), print six digits when second_part is non-zero and none otherwise, as MariaDB Connector/C does for 39, which gives the same strings as the text protocol. ps_fetch_time() gets the same change, though on MariaDB 13.0.2 I only got 39 for FROM_UNIXTIME() (TIMESTAMP) results.

The test compares the text and binary protocol results and skips unless the server reports 39 for FROM_UNIXTIME(). It fails without the fix on MariaDB 13.0.2 and skips on MySQL 8.4.13, and the other ext/mysqli, ext/pdo_mysql and ext/mysqlnd tests give the same results with and without the fix on both servers.

[ojuschugh1]

Changed to treat every decimals value above 6 as unknown precision, after @9EOR9's note in #16910 that 39 is a sentinel (31 in MySQL). It still prints no fraction when second_part is 0, since that's what the text protocol returns for FROM_UNIXTIME('1992.0').