bug: Incorrect serialization of numeric values

• asyncpg version: 0.29.0
• PostgreSQL version: 13
• Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
  the issue with a local PostgreSQL install?: no SaaS, yes reproducable with local postgres
• Python version: 3.10
• Platform: linux
• Do you use pgbouncer?: no
• Did you install asyncpg with pip?: yes
• If you built asyncpg locally, which version of Cython did you use?: none
• Can the issue be reproduced under both asyncio and
  uvloop?: yes

This happens when query selects a numeric column. Numbers like 10000, 100000, etc. get serialized in scientific notation. For example 10000 becomes 1E+4.

To reproduce the error, you can do the following:

Inside tests/test_codecs/test_numeric if 10000 is added in cases then the test fails, due to incorrect serialization logic.

    async def test_numeric(self):
        # Test that we handle dscale correctly.
        cases = [
            '0.001',
            '0.001000',
            '1',
            '1.00000',
            '10000', # new test case
        ]

fail error:

line 614, in test_numeric
    self.assertEqual(str(res), case)
AssertionError: '1E+4' != '10000'

Inizia in tests/test_codecs/test_numeric e aggiungi 10000 ai casi in test_numeric per riprodurre il fallimento. Traccia la logica di serializzazione numerica responsabile della restituzione di 1E+4 invece di 10000, quindi esegui il test e conferma che i casi esistenti continuino a superare il test mantenendo la stringa decimale prevista.