Deadlock on insert with cursors and fetchmany

### What happens?

DBAPI cursor with fetchmany causes deadlock when concurrent connections used within single process

### To Reproduce

```
from collections import deque, namedtuple
from typing import Sequence

import duckdb
import pyarrow
from loguru import logger
from tqdm import tqdm

schema = pyarrow.schema([
( 'id', pyarrow.int32()),
( 'name', pyarrow.string()),
( 'loves_food', pyarrow.bool_())
])

logger.info('Generating data')
data = deque()
for i in tqdm(range(4_000_000)):
data.append({
'id': i,
'name': 'Namey McNameFace',
'loves_food': True
})

arrow_table = pyarrow.Table.from_pylist(data, schema=schema)

conn = duckdb.connect('test.db')
conn.execute('CREATE OR REPLACE TABLE test (id INTEGER, name VARCHAR, loves_food BOOLEAN)')
logger.info('Inserting data')
conn.execute('INSERT INTO test SELECT * FROM arrow_table')

conn.execute('CREATE OR REPLACE TABLE test_write (id INTEGER, name VARCHAR, loves_food BOOLEAN)')

def get_data_in_chunks():
with conn.cursor() as cur:
cur.execute('SELECT * FROM test')
while True:
rows = cur.fetchmany(10000)
if not rows:
break
Row = namedtuple('Row', [c[0] for c in cur.description])
yield [Row(*r) for r in rows]

def insert_data_in_chunks(ins_data: Sequence):
with conn.cursor() as cur:
ins_table = pyarrow.Table.from_pylist(ins_data, schema=schema)
# this will stop executing at some point -- the exact number may be system-dependent, my mac is 2,240,000
# however, CPU usage will remain very high
cur.execute('INSERT INTO test_write SELECT * FROM ins_table')

num_processed = 0
for rs in get_data_in_chunks():
num_processed += len(rs)
logger.info(f'Got {len(rs)} records; {num_processed} processed so far')
dict_data = map(lambda r: r._asdict(), rs)
insert_data_in_chunks(rs)
```

### OS:

macOS (aarch64), Windows 11 (x64)

### DuckDB Package Version:

1.4.2

### Python Version:

3.12

### Full Name:

William Welch

### Affiliation:

Self

### What is the latest build you tested with? If possible, we recommend testing with the latest nightly build.

I have tested with a stable release

### Did you include all relevant data sets for reproducing the issue?

Yes

### Did you include all code required to reproduce the issue?

- [x] Yes, I have

### Did you include all relevant configuration to reproduce the issue?

- [x] Yes, I have

まず、提供された Python 再現コードを DBAPI カーソル、fetchmany、同時接続、および test_write への挿入を使って実行します。リポジトリのファイルやテストのエントリーポイントは指定されていません。ループがデッドロックや持続的な高 CPU 使用率なしに完了し、取得したすべての行が挿入されれば完了です。

索引モデルが issue の本文から書いたものです。