feat(storage): Support GCS RCU Bidirectional Read Integration Tests - DRAFT

[xlai20]

DRAFT: DO NOT REVIEW YET

Description

Implements live cloud integration tests for Test Suite 1: Bidirectional Read targeting Rapid Cache Ultra (RCU) / Rapid Storage in tests/storage/src/bidi_read.rs.

Key Test Cases Added

• Test 1 (test_multiple_ranged_read): Tests concurrent downloads across 4 non-overlapping segments (512 KiB total) over an open bidi read session using tokio::try_join!, verifying chunk data, total length, and CRC32C checksums.
• Test 2 (test_read_post_stream_close): Verifies stream lifecycle, EOF idempotency (next() == None), and cancellation/abort isolation when dropping an in-flight reader.
• Test 3 (test_zero_copy_read): Tests zero-copy buffer access using bytes::Bytes chunks across concurrent range readers.
• Test 4 (test_non_existent_bucket_read): Asserts appropriate NotFound or PermissionDenied error status when attempting to open a stream on a non-existent bucket.
• Test 5 (test_out_of_range): Verifies valid range read on open descriptor, followed by out-of-bounds offset reading returning OUT_OF_RANGE.
• Preserved Existing Tests: Maintained existing send, send_and_read, send_and_read_full, send_and_read_md5, and send_and_read_gzip test cases.
• Custom Endpoint Configuration: Added GOOGLE_CLOUD_TEST_STORAGE_ENDPOINT support to allow targeting preprod or emulator environments.

Verification

• cargo fmt --all -- --check & rustfmt --edition 2024 passed.
• cargo clippy --package integration-tests-storage --test driver --features run-integration-tests -- -D warnings passed cleanly.
• cargo test --package google-cloud-storage --test open_object_grpc passed (4 passed, 0 failed).
• cargo test --package integration-tests-storage --test driver --features run-integration-tests run_storage_bidi passed against live GCP project rust-sdk-testing.