Update EIP-7762: correct doubling rate

[Fibonacci747]

The text said “double every log_{1.125}(10) = 5.885 blocks”, which mixed doubling (×2) with a log argument for ×10. The 5.885 value actually corresponds to log_{1.125}(2). Updated the statement to “double every log_{1.125}(2) ≈ 5.886 blocks,” consistent with EIP-4844’s per-block growth cap (~1.125×) and the surrounding rationale that discusses climbing in factors of 2.