[WIP] feat: add s3 write support

[prantogg]

This PR addresses #70 - enables direct S3 streaming for generated data, eliminating local storage requirements for large-scale dataset generation. S3 URIs in --output-dir are automatically detected and routed to a streaming multipart upload implementation.

spatialbench-cli --scale-factor 1000 --output-dir s3://my-bucket/spatialbench/sf1000

• Implements streaming S3 writer with Write trait compatibility.
• Uses S3 multipart upload API with 32MB parts for efficient streaming. Small files (<5MB) use direct PUT requests.
• Multipart completion handled asynchronously via Tokio runtime. Built on object_store crate's AmazonS3Builder