feat(s3): add S3 bucket browsing as a VFS provider

[fecet]

Summary

• Implement a read-only S3 provider built on the object_store crate, allowing users to browse S3-compatible buckets natively within yazi
• Add ServiceS3 config with support for region, endpoint, credentials, force_path_style, and allow_http
• Extend Url enum and SchemeKind with an S3 variant; implement read_dir (paginated listing), metadata, and streaming read

Screenshot

Details

This builds on the VFS provider infrastructure from #3821. The S3 provider is currently read-only — write operations (copy, create, create_dir, etc.) return Unsupported.

Configuration example in yazi.toml:

[[vfs.services]]
name = "my-s3"
type = "s3"
region = "us-east-1"
endpoint = "https://s3.amazonaws.com"
# access_key_id = "..."
# secret_access_key = "..."
# force_path_style = false
# allow_http = false

Then browse via s3://my-s3/bucket-name/path/.