Fix building with upcoming fmt-10 library

[jan-kolarik]

As implicit conversions for enums were deprecated in fmt 10.0.0, we need to explicitly do the conversion for custom enums. See: https://github.com/fmtlib/fmt/blob/10.0.0/ChangeLog.rst?plain=1#L68

Also, using fmt 10, time_point<system_clock> contains seconds represented as a floating-point number. In order to drop the decimal places, we need to explicitly do the conversion. This is also conformant with the currently used fmt-9.1 docs: https://fmt.dev/9.1.0/syntax.html#chrono-format-specifications.

Bugzilla ticket: https://bugzilla.redhat.com/show_bug.cgi?id=2218180.
Closes #675.

[xvitaly]

time_point is a known regression: fmtlib/fmt#3430

I backported fix in fmt-10.0.0-2.fc39.

[jan-kolarik]

@xvitaly Oh, nice! Thanks for info, I will test it and eventually drop the commit.

[jan-kolarik]

Hmm, actually the commit seems needed in our case. The formatting of seconds remains changed even with fmt-10.0.0-2.fc39 installed (note that "expected" and "actual" are swapped in the output):

test_loggers.cpp:134:Assertion
Test name: LoggersTest::test_loggers
equality assertion failed
- Expected: 2020-02-25T04:25:06.000000000+0000 [25] INFO Info message
2020-02-25T04:25:07.000000000+0000 [25] DEBUG Debug message
2020-02-25T04:25:08.000000000+0000 [25] TRACE Trace message
2020-02-25T04:25:09.000000000+0000 [25] CRITICAL Critical message
2020-02-25T04:25:10.000000000+0000 [25] ERROR Error message
2020-02-25T04:25:11.000000000+0000 [25] WARNING Warning message
2020-02-25T04:25:12.000000000+0000 [25] NOTICE Notice message
2020-02-25T04:25:13.000000000+0000 [25] INFO Info message
2020-02-25T04:25:14.000000000+0000 [25] DEBUG Debug message
2020-02-25T04:25:15.000000000+0000 [25] TRACE Trace message
2020-02-25T04:25:16.000000000+0000 [25] INFO Info additional message

- Actual  : 2020-02-25T04:25:06+0000 [25] INFO Info message
2020-02-25T04:25:07+0000 [25] DEBUG Debug message
2020-02-25T04:25:08+0000 [25] TRACE Trace message
2020-02-25T04:25:09+0000 [25] CRITICAL Critical message
2020-02-25T04:25:10+0000 [25] ERROR Error message
2020-02-25T04:25:11+0000 [25] WARNING Warning message
2020-02-25T04:25:12+0000 [25] NOTICE Notice message
2020-02-25T04:25:13+0000 [25] INFO Info message
2020-02-25T04:25:14+0000 [25] DEBUG Debug message
2020-02-25T04:25:15+0000 [25] TRACE Trace message
2020-02-25T04:25:16+0000 [25] INFO Info additional message