fix(storage): Update offset on resumable upload retry

[cjc25]

When resumable uploads retry, they may observe a flush offset which is past the start of the current send (in fact the whole send might have already completed). In that case, we avoided re-sending unnecessary data, but we didn't update the offset to account for the data not sent.

[tritone]

Talked with @cjc25 ; test coverage for this will come via a fix in storage-testbench.

[cjc25]

The test failure here is only on "earliest version" (go 1.23.6) not "latest version" (go 1.24.0):

=== RUN   TestRetryTimeoutEmulated
=== RUN   TestRetryTimeoutEmulated/grpc
    client_test.go:2228: GetBucket: got unexpected error: rpc error: code = DeadlineExceeded desc = context deadline exceeded; want 503
    client_test.go:2233: GetBucket: got unexpected error rpc error: code = DeadlineExceeded desc = context deadline exceeded, want to match DeadlineExceeded.
=== RUN   TestRetryTimeoutEmulated/http
--- FAIL: TestRetryTimeoutEmulated (0.42s)
    --- FAIL: TestRetryTimeoutEmulated/grpc (0.21s)
    --- PASS: TestRetryTimeoutEmulated/http (0.21s)

Which is... surprising :). Maybe just flaky comparison, but I don't think related to this PR. I can look later.

[tritone]

The test failure here is only on "earliest version" (go 1.23.6) not "latest version" (go 1.24.0):

=== RUN   TestRetryTimeoutEmulated
=== RUN   TestRetryTimeoutEmulated/grpc
    client_test.go:2228: GetBucket: got unexpected error: rpc error: code = DeadlineExceeded desc = context deadline exceeded; want 503
    client_test.go:2233: GetBucket: got unexpected error rpc error: code = DeadlineExceeded desc = context deadline exceeded, want to match DeadlineExceeded.
=== RUN   TestRetryTimeoutEmulated/http
--- FAIL: TestRetryTimeoutEmulated (0.42s)
    --- FAIL: TestRetryTimeoutEmulated/grpc (0.21s)
    --- PASS: TestRetryTimeoutEmulated/http (0.21s)

Which is... surprising :). Maybe just flaky comparison, but I don't think related to this PR. I can look later.

This is somewhat surprising for the emulator but might just be a flake; I triggered a rerun.

[cjc25]

The test failure here is only on "earliest version" (go 1.23.6) not "latest version" (go 1.24.0):

=== RUN   TestRetryTimeoutEmulated
=== RUN   TestRetryTimeoutEmulated/grpc
    client_test.go:2228: GetBucket: got unexpected error: rpc error: code = DeadlineExceeded desc = context deadline exceeded; want 503
    client_test.go:2233: GetBucket: got unexpected error rpc error: code = DeadlineExceeded desc = context deadline exceeded, want to match DeadlineExceeded.
=== RUN   TestRetryTimeoutEmulated/http
--- FAIL: TestRetryTimeoutEmulated (0.42s)
    --- FAIL: TestRetryTimeoutEmulated/grpc (0.21s)
    --- PASS: TestRetryTimeoutEmulated/http (0.21s)

Which is... surprising :). Maybe just flaky comparison, but I don't think related to this PR. I can look later.

This is somewhat surprising for the emulator but might just be a flake; I triggered a rerun.

The issue is that we check specifically that the error is context.DeadlineExceeded, but this is a gRPC-layer DeadlineExceeded. I don't think that can be reliable: the context deadline is propagated to the server, so now there are two clocks, and the server might return a DeadlineExceeded error before the local context is actually cancelled.

I'll send a PR to check for gRPC errors too.

[cjc25]

#12092 to fix the flake