[rust] Add Fluss 1.x protocol support to the admin client

[gnuhpc]

What

Adds 27 new admin methods to FlussAdmin, consuming the message wrappers from #629/#630:

• Database/table extensions: list_database_summaries, alter_database, alter_table, get_table_stats
• KV snapshot operations: get_latest_kv_snapshots, get_kv_snapshot_metadata, create_kv_snapshot_lease, get_lake_snapshot
• ACL management: create_acls, list_acls, drop_acls
• Cluster configuration: describe_cluster_configs, alter_cluster_configs
• Server management: add_server_tag, remove_server_tag, rebalance, list_rebalance_progress, cancel_rebalance
• Producer offsets: register_producer_offsets, get_producer_offsets, delete_producer_offsets
• Monitoring: get_cluster_health, list_remote_log_manifests
• KV snapshots: list_kv_snapshots, release_kv_snapshot_lease, drop_kv_snapshot_lease

(The proto-compat fix for scanner.rs / admin.rs lives in #628 so that PR leaves the tree building.)

Stack

Part 4/6, stacked on #630 → #629 → #628. All target main.

🤖 Generated with Claude Code

[gnuhpc]

Rebased onto updated #630 and applied the same proto::*/Default cleanup the maintainer requested on #629 (#629 (review)) to every signature this PR adds. All 21 admin methods that previously leaked proto::Pb* in args or returns now take/return domain types. use crate::proto; is gone from admin.rs; only the pre-existing use crate::proto::GetTableInfoResponse; (from main) remains.

Response-side domain types added under crates/fluss/src/metadata/:

• cluster_health.rs — ClusterHealth
• kv_snapshot.rs — KvSnapshot, LatestKvSnapshots, RemotePathAndLocalFile, KvSnapshotMetadata, AcquireKvSnapshotLeaseResult, ActiveKvSnapshots
• lake_snapshot.rs — LakeBucketSnapshot, LakeSnapshotInfo (distinct from the existing LakeSnapshot used by get_latest_lake_snapshot)
• rebalance.rs — RebalanceProgress, TableRebalanceProgress, BucketRebalanceProgress, BucketRebalancePlan
• remote_log.rs — RemoteLogManifestEntry
• Extended config.rs (DescribeConfig), database.rs (DatabaseSummary), table_stats.rs (BucketStats/TableStats/BucketStatsError), acl.rs (CreateAclResult/DropAclsFilterResult/DropAclMatchingAcl), producer_offsets.rs (ProducerOffsets)

For trivially-shaped responses (single field), methods now return the primitive directly instead of wrapping — e.g. rebalance returns String (the rebalance id), register_producer_offsets returns Option<i32>, list_acls returns Vec<AclInfo>, list_remote_log_manifests returns Vec<RemoteLogManifestEntry>.

alter_table parameter fix (same drop-silently-features class as target_columns in #629): previously took only config_changes + add_columns and hardcoded vec![],vec![],vec![] for drop/rename/modify columns. Now takes an AlterTableChanges bundle struct (avoids clippy::too_many_arguments) exposing all 5 change types, plus ignore_if_not_exists is now a parameter instead of hardcoded false.

#[derive(Default)] not present anywhere in this PR (admin.rs has none); the wrappers consumed are already cleaned up on #629/#630.

cargo build + clippy (-D warnings) + 556 unit tests pass locally. Pushed 29a4d0b.