Honor Apache X-Request-Start header containing microseconds

[Capncavedan]

At my work we recently switched to nginx from Apache, and were puzzled why we began seeing errors to do with rack-timeout's wait_timeout behavior when we hadn't before. We'd had the X-Request-Start header set on Apache for some time (years)

I tracked it down to the Apache-formatted header with microseconds, e.g. "t=" + 16 digits like t=1700173924763384, not being honored, as mentioned here.

This PR adds that capability, with a test, and also adds notes to docs/settings.md, UPGRADING.md, and CHANGELOG.md

First commit contains two lines I needed to add to be able to run the project's tests with rake.

[wuputah]

looks good. I'd like to know the tests pass, and I haven't run them manually, and I'm not exactly sure how to get them to run on your PR.

[Capncavedan]

@wuputah re: running the tests - after running bundle install in the code's directory, I am able to run the tests with rake:

[wuputah]

Ah sorry, I mean here on GitHub (CI).There should really be an easier way to approve this.

[Capncavedan]

@wuputah ah, gotcha, my misunderstanding!

[wuputah]

Workflow runs that have been awaiting approval for more than 30 days are automatically deleted.

If possible, can you rebase, force-push, and see if that lets me run the workflow? I think you wont need the changes in 7f78737 anymore.

[wuputah]

There's no bug in the implementation itself, but the tests are intermittently failing because time_in_usec needs 0-padding for the usec. You can see below that the string does not always have the same number of digits.

irb(main):006> time_in_usec(Time.now - 100)
=> "1715877828162572"
irb(main):007> time_in_usec(Time.now - 100)
=> "1715877828853808"
irb(main):008> time_in_usec(Time.now - 100)
=> "1715877829418922"
irb(main):009> time_in_usec(Time.now - 100)
=> "1715877829958034"
irb(main):010> time_in_usec(Time.now - 100)
=> "1715877830460281"
irb(main):011> time_in_usec(Time.now - 100)
=> "171587783114512"
irb(main):012> time_in_usec(Time.now - 100)
=> "1715877831583129"
irb(main):013> time_in_usec(Time.now - 100)
=> "1715877832181671"
irb(main):014> time_in_usec(Time.now - 100)
=> "1715877832857735"
irb(main):015> time_in_usec(Time.now - 100)
=> "1715877835515973"

[wuputah]

fix for time_in_usec

[Capncavedan]

@wuputah thanks for seeing this one across the finish line