test: internal: log: fix failures caused by timing issue.

[pwhelan]

Summary

The flb-it-log is failing sporadically. I believe this is because initially time is counted from 1 second before the message is first cached for both messages being test, TEST_RECORD_1 and TEST_RECORD_2.

[ FAILED ]
  log.c:18: Check (start + timeout) >= now... failed
    clock error, unsuppresed log: now=1712179281, timeout=1712179280, diff=1
  log.c:110: Check ret == 0... failed
  log.c:18: Check (start + timeout) >= now... failed
    clock error, unsuppresed log: now=1712179281, timeout=1712179280, diff=1
  log.c:114: Check ret == 0... failed
Test cache_one_slot...                          
[ OK ]
FAILED: 1 of 2 unit tests has failed.

Only a single failure is registered even though the loop occurs twice. This lines up with the idea that it is an off-by-one caused by starting the clocks one second after initially sending the message(s) to be suppressed by the log cache.

This fix simply starts counting time for each record right before emitting each one.

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Testing
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[pwhelan]

Apparently out_http also can suffer from flaky results:

Test in_http...                                 [ FAILED ]
  out_http.c:1157: Check num > 0... failed
    no outputs
FAILED: 1 of 15 unit tests has failed.

I'll see if I can get around to that one later. At the very least this PR did not fail in the flb-it-log test.