Invalid result of TIME to TIMESTAMP cast for high precisions

[findepi]

The value renders correctly (appears to be correct):

presto> SELECT CAST(TIME '12:34:56.55555555' AS TIMESTAMP(7));
            _col0
-----------------------------
 2020-10-29 12:34:56.5555556
(1 row)

but actual runtime value is not correct:

presto> SELECT CAST(TIME '12:34:56.55555555' AS TIMESTAMP(7)) = TIMESTAMP '2020-10-29 12:34:56.5555556';
 _col0
-------
 false
(1 row)

[findepi]

The example is taken from existing test:

assertThat(assertions.expression("CAST(TIME '12:34:56.55555555' AS TIMESTAMP(7))")).matches("TIMESTAMP '2020-05-01 12:34:56.5555556'");

this reveals a generic deficiency in our testing methodology.

cc @martint