fix(context): remove unreachable zero-denominator check in fake_exponential

[VolodymyrBg]

• Remove the redundant if denominator == 0 { return 0; } in fake_exponential.
• The function already asserts denominator != 0, so the branch is never executed.
• The denominator originates from protocol constants (BLOB_BASE_FEE_UPDATE_FRACTION_*) and config fallback, both guaranteed non-zero.
• Keeping the check was contradictory (assert panics vs returning 0) and introduced dead code

[codspeed-hq]

CodSpeed Performance Report

Merging #3039 will not alter performance

_{Comparing VolodymyrBg:fix/fake_exponential-dead-zero-check (e05801c) with main (a32f8f4)}

Summary

✅ 173 untouched