db: produce the FlushEnd event after installing readState

[sumeerbhola]

This helps unit tests that use the callback to trigger a
read using an iterator with IterOptions.OnlyReadGuaranteedDurable.

Informs cockroachdb/cockroach#77046

[cockroach-teamcity]

This change is 

[nicktrav]

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @sumeerbhola)

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compaction.go, line 1454 at r1 (raw file):

	d.mu.versions.incrementCompactionBytes(-c.bytesWritten)

	info.TotalDuration = d.timeNow().Sub(startTime)

I take it we don't want to include the time it takes to update the read state and table stats?

[sumeerbhola]

TFTR!

[sumeerbhola]

Reviewable status: 0 of 1 files reviewed, 1 unresolved discussion (waiting on @nicktrav)

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compaction.go, line 1454 at r1 (raw file):

Previously, nicktrav (Nick Travers) wrote…

I take it we don't want to include the time it takes to update the read state and table stats?

what I did was not principled, even though this part should be cheap (unlike creating a new Version) -- fixed now.