Clarify overflow analysis for maxDim-constrained image dimensions

[Copilot]

Addresses review feedback on PR #280 regarding potential integer overflow in width * height * getC() expression when checking image dimensions.

Analysis

With maxDim = 65536, the maximum product width * height is 4,294,967,296, which fits in 64-bit size_t. Even with typical channel counts (1-4), the expression width * height * getC() doesn't overflow size_t before the INT_MAX comparison.

Overflow would only occur if:

• Running on 32-bit systems (where size_t is 32-bit), or
• numChannels exceeds ~4 million

The existing check is safe on 64-bit systems with reasonable channel counts. The suggested overflow-safe multiplication approach would add defensive checks that may not be necessary given the maxDim constraint, though they would provide additional safety on 32-bit platforms.

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