Calculate fake import start from import end

[phil-davis]

Q	A
Bug fix?	Y
New feature?	N
Related user documentation PR URL	N/A
Related developer documentation PR URL	N/A
Issues addressed (#s or URLs)	#5059
BC breaks?
Deprecations?

Description:

1. Calculate fakeImportStartDate() as an offset from the end date-time, rather than the current date-time. That should avoid rounding issues due to the real time delay between setting end date-time and then making the adjustment to fake the start date-time.

2. Fix a bunch of comment typos in Import.php while we are here.

Steps to reproduce the bug:

1. run the unit tests lots of times
2. see the failure:

There was 1 failure:
1) Mautic\LeadBundle\Tests\Entity\ImportTest::testGetRunTimeSeconds
Failed asserting that 601 is identical to 600.

Steps to test this PR:

1. run the unit tests lots more times
2. do not see any failure

[phil-davis]

I suspect that for this test to have failed, it needed to start at something like 12:15:10.995 and have the start time backed up 600 seconds to 12:05:10.995 and then the end time like 12:15:11.005
I think the fractional seconds disappear in the DateTime object, so it ends up with start time 12:05:10 and end time 12:15:11 and the elapsed time is calculated as 601 seconds.

[phil-davis]

Put a small delay before here in the original code, e.g.:

usleep(100000);

and then run the test and you get about 10% fails.

With just the natural compute time delay it is a bit difficult to get the "random" fail.

[phil-davis]

Rebased

[phil-davis]

Rebased on top of #5367 so that CI should pass.

[phil-davis]

Rebased again

[Hadamcik]

Works for me, even after 1000 runs of test, nothing brakes (I had usleep(100000); added)