refactor(core): Split buffer logic from underlying storage operations

[Xuanwo]

This PR splits buffer logic from underlying storage operations to make them more clear. This PR only migrates multipart uploads and append object for now. We can migrate gcs upload and azblob upload in next PRs.

[Xuanwo]

  2023-08-22T09:37:51.848707Z ERROR opendal::services: service=s3 operation=Writer::close path=bc2a53e0-e316-4547-9761-00f1c4bc4297 written=51547533 -> data close failed: Unexpected (permanent) at Writer::close => S3Error { code: "InvalidPart", message: "All non-trailing parts must have the same length.", resource: "", request_id: "" }

Context:
   uri: ***/***/83d71cb1-c866-428c-b98d-b3524bd4f884/bc2a53e0-e316-4547-9761-00f1c4bc4297?uploadId=AJ1CTqPx%2Bfaq%2BlgT7QVTh%2BFIUs1948K2Q4I%2FqZJIVrYJx71WCHrMtXAzuC5bq07jYc4Q37Zx3vYkH69e5gIsqilzlmcPUwuqjzosxCJy1yBd09fsWFctpqcnbRLsmi3Iy7SRmkQ3IqeTsnlbXV0eKkPTGE2U6EMsD%2F2Lhpok7qZ%2BMUM84VgwunX2%2FpQpmSnXflykOfIQ9WV%2BOjhOv6%2F7ptB0NgQseVkVCLdreM8IPUJYIENWvPXkFhlZbEojnZ9ibrEWAmdADwWcGhhARG%2BdfhQbyVA%2Bj9eLWyL1RI2B%2F0n61OV4v%2BZoAC7L3PqmcOvRdOtsOP5wMNrdISEEo%2Be%2Btv4%3D
   response: Parts { status: 400, version: HTTP/1.1, headers: {"date": "Tue, 22 Aug 2023 09:37:51 GMT", "content-type": "application/xml", "content-length": "145", "connection": "keep-alive", "server": "cloudflare", "cf-ray": "7faa23b91daf3b12-IAD"} }
   service: s3
   path: bc2a53e0-e316-4547-9761-00f1c4bc4297

Special requirement of r2

[Xuanwo]

cc @suyanhanx, please take another look, thanks!

[suyanhanx]

Thanks.