feat(spanner): add ISO8601 duration support to spanner::Interval

[devbww]

In the pre-release specification for TypeCode::INTERVAL, the wire encoding was given as a string in "intervalstyle == postgres" format, and spanner::Interval was implemented accordingly.

By the time the feature was released in the backend, this encoding changed to be a string in ISO8601 duration format.

So:

• Change Interval::operator std::string() to return a ISO8601 duration string.
• Extend MakeInterval(absl::string_view) to recognize ISO8601 duration format.
• Update and extend the test cases accordingly.

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This change is 

[scotthart]

Reviewed 2 of 3 files at r1, all commit messages.
Reviewable status: 2 of 3 files reviewed, all discussions resolved

[scotthart]

Thanks for these updates!

My understanding is that Interval support has been rolled out in production, so at some point in the near future we'll look at adding Interval to google/cloud/spanner/value.[h|cc] and some integration tests.

[scotthart]

/gcbrun

[devbww]

Thanks for these updates!

You're welcome.

My understanding is that Interval support has been rolled out in production,

That is my understanding too.

so at some point in the near future we'll look at adding Interval to google/cloud/spanner/value.[h|cc]

I already have that change lined up. It is congruent to the already-sent UUID one.

and some integration tests.

Yes, but you'll be on your own there (and for UUID) as I don't have the resources to run integration tests. My plan was to file two issues (Interval and UUID) pointing at the appropriate tests.

[codecov]

Codecov Report

Attention: Patch coverage is 96.77419% with 7 lines in your changes missing coverage. Please review.

Project coverage is 92.90%. Comparing base (6e34f52) to head (1b0b85f).
Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
google/cloud/spanner/interval_test.cc	93.06%	7 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main   #15077    +/-   ##
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  Coverage   92.90%   92.90%            
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  Files        2354     2354            
  Lines      210365   210488   +123     
========================================
+ Hits       195441   195564   +123     
  Misses      14924    14924            

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[scotthart]

/gcbrun

[scotthart]

/gcbrun