feat: Add explain support for lance

[Xuanwo]

This PR will add explain support for lance

D EXPLAIN (format json)  SELECT count(*) FROM 'test/test_data.lance' WHERE age > 30;

┌─────────────────────────────┐
│┌───────────────────────────┐│
││       Physical Plan       ││
│└───────────────────────────┘│
└─────────────────────────────┘
[
    {
        "name": "UNGROUPED_AGGREGATE",
        "children": [
            {
                "name": "LANCE_SCAN ",
                "children": [],
                "extra_info": {
                    "Lance Path": "test/test_data.lance",
                    "Lance Explain Verbose": "false",
                    "Lance Pushed Filter Parts": "1",
                    "Lance Filter IR Bytes (Bind)": "37",
                    "Lance Plan (Bind)": [
                        "ProjectionExec: expr=[id@0 as id, name@4 as name, age@1 as age, score@2 as score]",
                        "  Take: columns=\"id, age, score, _rowid, (name)\"",
                        "    CoalesceBatchesExec: target_batch_size=8192",
                        "      LanceRead: uri=Users/xuanwo/conductor/workspaces/lance-duckdb/riga/test/test_data.lance/data, projection=[id, age, score], num_fragments=1, range_before=None, range_after=None, row_id=true, row_addr=false, full_filter=age > Int64(30), refine_filter=age > Int64(30)"
                    ],
                    "Projections": "",
                    "Filters": "age>30",
                    "Estimated Cardinality": "1"
                }
            }
        ],
        "extra_info": {
            "Aggregates": "count_star()"
        }
    }
]

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Parts of this PR were drafted with assistance from Codex (with gpt-5.2) and fully reviewed and edited by me. I take full responsibility for all changes.