fix: Correct off-by-one error in ExecPlan countLines() method

[Copilot]

The countLines() method in the ExecPlan document was overcounting lines by 1 due to using feof() as the loop condition, which continues one iteration after EOF is reached.

Changes

• Modified loop condition from while (!feof($handle)) to while (($line = fgets($handle)) !== false)
• Ensures only lines actually read are counted

// Before: counts one extra line after EOF
while (!feof($handle)) {
    fgets($handle);
    $count++;
}

// After: counts only lines successfully read
while (($line = fgets($handle)) !== false) {
    $count++;
}

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