Use explicit size_t for loop variables to avoid signed/unsigned comparison warnings

[Copilot]

Addresses review feedback on loop variable types in EstimatorBase.cpp that could trigger signed/unsigned comparison warnings.

Changes

• Changed loop variable declarations from auto to explicit size_t types
• Ensures type compatibility with array indices (roi[0], roi[1], roi[2], roi[3])
• Prevents potential signed/unsigned comparison warnings at lines 202-206

// Before: auto deduces to int from literal 0
for (auto y = 0; y < roi[3]; ++y) {
    for (auto x = roi[0]; x < roi[2]; ++x) {
        // ...
    }
}

// After: explicit size_t matches array index types
for (size_t y = 0; y < roi[3]; ++y) {
    for (size_t x = roi[0]; x < roi[2]; ++x) {
        // ...
    }
}

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