fix: track IO::File handles in array to support concurrent opens

[toddr-bot]

What

Fix _io_file_mock_open to use the {'fhs'} array instead of the scalar {'fh'} slot for tracking open IO::File handles.

Why

Opening a second IO::File handle to the same mocked file overwrote the first handle's tracking reference, making it invisible to _fh_to_file. This broke stat(), truncate(), and any filehandle-to-path lookup on the first handle — returning EBADF instead of the file's metadata.

The {'fh'} scalar slot is also used by __opendir for directory handles. While files and directories don't collide in practice, using the same slot for two different purposes is a latent conflict.

How

Changed _io_file_mock_open from:

$mock_file->{'fh'} = $fh;
Scalar::Util::weaken( $mock_file->{'fh'} ) if ref $fh;

to the {'fhs'} array pattern already used by __open:

$mock_file->{'fhs'} //= [];
push @{ $mock_file->{'fhs'} }, $fh;
Scalar::Util::weaken( $mock_file->{'fhs'}[-1] ) if ref $fh;

Testing

• Added 7 new assertions in t/io_file_compat.t covering multiple concurrent IO::File handles and handle lookup surviving peer close
• Full suite: 1593 tests, zero regressions (only pre-existing fh-ref-leak.t failure)

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Quality Report

Changes: 2 files changed, 44 insertions(+), 3 deletions(-)

Code scan: clean

Tests: failed (4 Failed, 94 test)

Branch hygiene: clean

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