Add S3 write support with hybrid storage for BP5

[eisenhauer]

S3 Multipart Upload

• FileAWSSDK write support using S3 multipart upload API
• Zero-copy uploads via AWS SDK's PreallocatedStreamBuf
• Configurable part sizes (min_part_size, max_part_size)
• Buffering for small writes to meet S3's 5MiB minimum

Hybrid Storage (Local Metadata + S3 Data)

• New DataTransport engine parameter to route data files to S3
• Metadata files (md.idx, md.0, mmd.0) stay local for fast access
• BP5Reader/Writer: separate FilePool for metadata vs data
• S3 parameters: S3Endpoint, S3Bucket

Other Fixes

• ParseArgs: quoted value support for URLs with colons
• FileAWSSDK: proper path handling with bucket parameter
• Transport cleanup order fix in DoClose

Usage

io.SetEngine("BP5");
io.SetParameter("DataTransport", "awssdk");
io.SetParameter("S3Endpoint", "http://localhost:9000");
io.SetParameter("S3Bucket", "mybucket");

[pnorbert]

So the metadata is always stored locally?

[eisenhauer]

In this implementation, yes. No reason why we couldn't have a pure S3 version, though some things probably get a little messier. For example, if you were actively writing, the metadata files would have to go above 5Mb before we could write even a portion of them. No issue if we have a normal shutdown, but the possibility of crash recovery would be virtually eliminated. But easy to have a copy-to-S3 and/or copy-from-s3 utility, things like that.