feat(sdk): select OSS upload strategy by size

[pfwang80s]

Context

The Swift SDK should keep using the official Alibaba OSS SDK, but it needs to choose PutObject or MultipartUpload from the file size instead of always exercising the multipart path.

What Changed

• Add PutObject support to the Swift OSS session and route files with fileSize <= partSizeBytes through PutObject.
• Keep files larger than partSizeBytes on the existing MultipartUpload path.
• Persist enough state to resume PutObject uploads by checking remote object metadata before completing the business upload.
• Update upload coordinator tests for small-file PutObject, exact-boundary PutObject, multipart, restart, and resume behavior.
• Update real Aliyun integration tests so small and exact-boundary uploads reject multipart events while large uploads require multipart events.
• Allow real Aliyun tests to override request timeout with DGW_REAL_REQUEST_TIMEOUT_SECONDS for 64 MiB+ payloads.

Validation

• swift test --no-parallel
• git diff --check
• Dev ACK Swift SDK E2E: swift test --no-parallel --filter realAliyun with 9 real Aliyun tests passing, including runtime upload, list objects, PutObject events, exact-part-size PutObject events, multipart events, config-store upload, resume, abort/delete local snapshot, and device init/reinit upload.

Risks and Rollout

• Risk: PutObject now becomes the default small-file path, so behavior changes from multipart-specific event streams to a single uploading-part event for small files.
• Rollout or rollback: roll out as a Swift SDK update; rollback by reverting this PR to restore the previous multipart-only data path.