perf: optimize constant-base exp

[DaniPopes]

Adds EXP peepholes for constant bases with dynamic exponents. The optimized cases cover zero, one, minus one, and power-of-two bases while preserving dynamic gas accounting through a new exp_gas builtin that only charges the exponent-dependent gas.

The test matrix now generates const/dynamic operand combinations for binary and ternary opcode tests, which covers the new EXP paths and broadens existing peephole coverage. This also fixes constant memory operand handling so zero-length memory operations still require a valid offset when the interpreter would validate it.

Tests: cargo fmt --all, cargo cl -q, TMPDIR=$PWD/target/tmp cargo nextest run -p revmc-codegen.

[codspeed-hq]

Merging this PR will not alter performance

✅ 65 untouched benchmarks
⏩ 24 skipped benchmarks¹

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_{Comparing dani/exp-const-base-peepholes (a76c323) with main (03a9a10)}

Footnotes

1. 24 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩