Regression in copy records performance between 0.30.0 and 0.31.0

Nadie ha tomado este issue todavía.

When run on different versions (0.30.0 vs 0.31.0), the following script reproduces the issue and consistently shows a performance regression of approximately 22%:

```py
import asyncio
import asyncpg
import time

COUNT = 5_000

async def run():
conn = await asyncpg.connect("postgresql://user:password@localhost/postgres")

await conn.execute("CREATE TABLE IF NOT EXISTS users (id SERIAL PRIMARY KEY, username TEXT, email TEXT, age INT)")

RECORDS = [("John Doe", "john.doe@example.com", 42)] * 10_000

start = time.perf_counter()
for _ in range(COUNT):
await conn.copy_records_to_table("users", records=RECORDS, columns=["username", "email", "age"])
end = time.perf_counter()

await conn.close()

return end - start

if __name__ == "__main__":
total = asyncio.run(run())
print(f"Total time: {total:.5f} seconds")
print(f"Average time per loop: {total / COUNT:.8f} seconds")
```

```
(common) [e.lee@OC0000842]$ pip install asyncpg==0.30.0
(common) [e.lee@OC0000842]$ python -m example
Total time: 89.15468 seconds
Average time per loop: 0.01783094 seconds

(common) [e.lee@OC0000842]$ pip install asyncpg==0.31.0
(common) [e.lee@OC0000842]$ python -m example
Total time: 108.57080 seconds
Average time per loop: 0.02171416 seconds
```

Comienza ejecutando el script de asyncio proporcionado con asyncpg 0.30.0 y 0.31.0 contra PostgreSQL, confirmando la diferencia de tiempo reportada en copy_records_to_table. Sigue la ruta de copy_records_to_table para identificar qué cambió entre esas versiones; se considera terminado cuando la regresión esté explicada y el benchmark ya no muestre la ralentización reportada.

Escrito por el modelo de indexación a partir del texto del issue.