feat(storage): implement API, request builders, integration tests

[vsharonlynn]

This PR comes after PR #5956.

[gemini-code-assist]

Code Review

This pull request implements bidirectional streaming writes (Bidi Write) for Google Cloud Storage, introducing the AppendableObjectWriter along with request builders OpenAppendableObject and ReopenAppendableObject to support appending data to objects. It includes a background Worker to manage the gRPC stream, a Connector to handle connection handshakes and routing redirects, and comprehensive unit and integration tests. The review feedback highlights two opportunities in connector.rs to improve error handling by replacing .expect() calls with safe error propagation using ? when converting parameters to proto format.

[codecov]

Codecov Report

❌ Patch coverage is 85.81699% with 217 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.48%. Comparing base (5e91002) to head (5e066c1).

Files with missing lines	Patch %	Lines
src/storage/src/storage/open_appendable_object.rs	45.04%	111 Missing ⚠️
...rc/storage/src/storage/reopen_appendable_object.rs	68.64%	37 Missing ⚠️
src/storage/src/storage/bidi_write/worker.rs	82.03%	23 Missing ⚠️
src/storage/src/storage/stub.rs	0.00%	18 Missing ⚠️
src/storage/src/storage/bidi_write/transport.rs	96.03%	12 Missing ⚠️
src/storage/src/storage/bidi_write/connector.rs	98.03%	10 Missing ⚠️
src/storage/src/storage/bidi_write/redirect.rs	95.50%	4 Missing ⚠️
src/storage/src/storage/transport.rs	97.14%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5957      +/-   ##
==========================================
- Coverage   97.72%   97.48%   -0.24%     
==========================================
  Files         242      250       +8     
  Lines       60882    62351    +1469     
==========================================
+ Hits        59495    60782    +1287     
- Misses       1387     1569     +182     

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[vsharonlynn]

I ran

$ cargo +nightly public-api -p google-cloud-storage diff origin/main..HEAD

The output is:

Removed items from the public API
=================================
(none)

Changed items in the public API
===============================
(none)

Added items to the public API
=============================
(none)

[coryan]

This is too large for a single PR, please split.

[vsharonlynn]

This is too large for a single PR, please split.

Sorry about this. I have chained PRs, this has changes from #5956. Because my branches are in my fork, I can't diff this branch from the #5956 branch in a PR into this repository.

One way I found on how to view only the changes for this PR is to select the commits that don't belong to the previous PR:

Happy to split it up if this still looks too large.

Another way is for us to wait until the previous PR is merged, then I'll rebase this before you take a look.

Please let me know if there is a more efficient way to do this...

Thank you.

[coryan]

Another way is for us to wait until the previous PR is merged, then I'll rebase this before you take a look.

Yes, that works for me.

Please let me know if there is a more efficient way to do this...

Support for stacked PRs (allegedly in the works at GitHub) may help, but I do not think that is available to us yet.

Normally we keep stacked PRs as draft. They are useful to give reviewers a sense of the overall change, but too large to review. Reviewing after a rebase is far more practical.