feat(copy): add recursive same-endpoint remote copy

[cxymds]

Related issue

Closes rustfs/backlog#1439
Parent roadmap: rustfs/backlog#1370
Depends on merged multipart copy primitive PR #301.

Background and user impact

Recursive remote-to-remote copy previously stopped at the CLI boundary even though RustFS now exposes the required same-endpoint server-side copy primitives. Users could not safely copy complete prefixes without scripting individual object operations.

Solution

• Traverse and paginate the complete source prefix before any mutation, then produce deterministic source-to-destination mappings.
• Reject overlapping prefixes, self copies, duplicate destinations, missing pagination tokens, and repeated pagination tokens during preflight.
• Reuse one S3 client pool per alias and the shared transfer executor for bounded concurrency, rate limiting, retry policy, and deterministic outcomes.
• Route objects at or below 5 GiB through CopyObject and larger objects through multipart server-side copy with source identity checks.
• Support dry run, continue-on-error, fail-empty, explicit skip-existing behavior, logical-byte progress, and deterministic summaries.
• Preserve source/destination versions and multipart upload IDs in human results, and retain abort cleanup details after failures or cancellation.
• Make cancellation race-safe across scheduling, rate waits, retry backoff, small CopyObject, and multipart cleanup; interrupted work is counted as cancelled and exits 130.
• Add the RustFS beta.10 recursive-copy integration smoke test.

Compatibility

• Cross-alias and cross-endpoint streaming copy remain out of scope.
• Planned/bulk JSON output remains explicitly unsupported until a versioned output contract is introduced.
• No protected CLI, JSON, exit-code, or configuration contract files are changed.

Validation

• cargo fmt --all --check
• cargo clippy --workspace --all-targets -- -D warnings
• CARGO_BUILD_JOBS=2 cargo test --workspace
• Recursive remote-copy black-box suite: 11 tests, including 1001-object pagination, mapping, overlap, empty prefix, skip-existing, partial failure, 5 GiB multipart routing, abort cleanup, and SIGINT exit 130.
• Flake check: recursive suite passed five consecutive full runs before final additions; final full workspace run passed with all 11 cases.