Test 1 (English headers + BOM):
Array
(
    [0] => Array
        (
            [campaign_id] => 1234567
            [campaign_name] => Test Campaign
            [date] => 2026-01-15
            [impressions] => 100
            [clicks] => 10
            [cost] => 50
            [avg_cpc] => 0.5
        )

)

Test 2 (Russian headers - legacy support):
Array
(
    [0] => Array
        (
            [campaign_id] => 7654321
            [campaign_name] => Русская Кампания
            [date] => 2026-01-14
            [impressions] => 200
            [clicks] => 20
            [cost] => 100
            [avg_cpc] => 5
        )

)

PASS: Test 1 successful
PASS: Test 2 successful