FileIO.load(file_directories=...) reuses first file's inferred format for all files

Problem

When FileIO.load() is called with file_directories and format=None, the format inferred from the first file is reused for every subsequent file, corrupting reads on mixed-format directories.

File

mage_ai/io/file.py lines 45-49:

for fp in file_paths:
    if format is None:
        format = self._get_file_format(fp)
    df = self._read(fp, format, **kwargs)

After iter 1, format is set, so if format is None is False for iter 2+.

Steps

1. Create dir with a.csv and b.parquet.
2. FileIO().load(file_directories=['dir'])

Expected

Each file read with its own inferred format.

Actual

b.parquet read as CSV; pandas raises UnicodeDecodeError or ParserError.

Env

mage-ai 0.9.79, Python >=3.10 (per setup.py:21,36).

Fix

Move format = None reset inside the loop, or use a local var per iteration.

Thanks for maintaining mage-ai/mage-ai!