Add BinaryColumnToVarbinaryRector for TYPE_VARBINARY migration

[dereuromark]

Summary

Adds a Rector rule to help users upgrade migration files for CakePHP 6.0 where TYPE_VARBINARY was added.

Related: cakephp/cakephp#19258

Transformations

Fixed-length binary (with fixed attribute):

// Before
$table->addColumn('hash', 'binary', ['length' => 32, 'fixed' => true]);

// After
$table->addColumn('hash', 'binary', ['length' => 32]);

Variable-length binary (without fixed attribute):

// Before
$table->addColumn('data', 'binary', ['length' => 255]);

// After
$table->addColumn('data', 'varbinary', ['length' => 255]);

Notes

• This rule targets addColumn() calls in migration files
• The fixed attribute is removed since binary type is now always fixed-length
• Columns without fixed => true are converted to varbinary type