Add REPL example (#553)

Both as a literal Rust example and for debugging purposes.

Demo:

![CleanShot 2025-07-23 at 15 40
14](https://github.com/user-attachments/assets/2ea57fef-26c4-44ff-9e03-7ebdf41b089a)

For example, here's how it can be used to reproduce #396

```
❯ cargo run --example repl
   Compiling duckdb v1.3.2 (/Users/mathias/devel/duckdb/duckdb-rs/crates/duckdb)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.48s
     Running `target/debug/examples/repl`
duckdb-rs v1.3.2 🦀
Type '.help' for help.
> SELECT (i*10^i)::varchar AS str FROM range(5) tbl(i)
+---------+
| str     |
| Utf8    |
+---------+
| 0.0     |
| 10.0    |
| 200.0   |
| 3000.0  |
| 40000.0 |
+---------+
> SET produce_arrow_string_view = true;
> SELECT (i*10^i)::varchar AS str FROM range(5) tbl(i)
+---------+
| str     |
| Utf8    |
+---------+
| 0.0     |
| 10.0    |
| 200.0   |
| 3000.0  |
| 40000.0 |
+---------+
> set arrow_output_version = '1.4'
> SELECT (i*10^i)::varchar AS str FROM range(5) tbl(i)
+----------+
| str      |
| Utf8View |
+----------+
| 0.0      |
| 10.0     |
| 200.0    |
| 3000.0   |
| 40000.0  |
+----------+
```

Debug mode will output more info:

```
> .debug
> SELECT (i*10^i)::varchar AS str FROM range(5) tbl(i)
+----------+
| str      |
| Utf8View |
+----------+
| 0.0      |
| 10.0     |
| 200.0    |
| 3000.0   |
| 40000.0  |
+----------+
[crates/duckdb/examples/repl.rs:173:13] &rbs = [
    RecordBatch {
        schema: Schema {
            fields: [
                Field {
                    name: "str",
                    data_type: Utf8View,
                    nullable: true,
                    dict_id: 0,
                    dict_is_ordered: false,
                    metadata: {},
                },
            ],
            metadata: {},
        },
        columns: [
            StringViewArray
            [
              "0.0",
              "10.0",
              "200.0",
              "3000.0",
              "40000.0",
            ],
        ],
        row_count: 5,
    },
]
```

Author: mlafeldt

.gitignore

@@ -25,3 +25,5 @@
 crates/libduckdb-sys/duckdb-sources/*
 crates/libduckdb-sys/duckdb/
 crates/libduckdb-sys/._duckdb
+
+.duckdb_rs_history