perf: optimize loop increment gas cost in GasPriceOracle

[forumevi]

Summary

Optimizes gas consumption in GasPriceOracle._getCalldataGas by wrapping the loop counter increment in an unchecked block.

Since i < length is enforced by the loop condition, i++ cannot overflow uint256. Bypassing default overflow checks saves gas per byte iteration.

[cb-heimdall]

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