fix: surface storage interface expectations correctly.

[frankyn]

cc: @dmitry-fa , @athakor based on pending PRs.

We will continue to update the Storage interface and mark it as InternalExtensionOnly.

[codecov]

Codecov Report

Merging #241 into master will not change coverage.
The diff coverage is n/a.

@@ Coverage Diff @@ ## master #241 +/- ## ========================================= Coverage 63.50% 63.50% Complexity 540 540 ========================================= Files 30 30 Lines 4762 4762 Branches 427 427 ========================================= Hits 3024 3024 Misses 1578 1578 Partials 160 160 

Impacted Files	Coverage Δ	Complexity Δ
...rc/main/java/com/google/cloud/storage/Storage.java	80.57% <ø> (ø)	0.00 <0.00> (ø)

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[dmitry-fa]

This fix is a good solution for the situation with extending the Storage interface. My question, is this change allowed?
Quoting: InternalExtensionOnly

Adding this annotation to an API is considered API-breaking.

[frankyn]

Hi @dmitry-fa, +1 to being allowed. I went through internal review/discussion with folks and it was a trade-off decision at this point. The annotation is only documentation and doesn't change how the interface can be used.

Also acknowledging that this library doesn't follow Semantic versioning strictly but looking for input from @JesseLovelace and @crwilcox on this point. I may end up removing it until later.