perf: optimize solidity verification contract

[xBA5ED]

When I was looking at the sp1-project-template I spotted some ways to optimize the contract a bit more and simplify it a bit at the same time. I followed the source of the contract back to this repo.

The following is the gas change for the tests when the changes are applied to the template repository:

Ran 2 tests for test/Fibonacci.t.sol:FibonacciTest
[PASS] testFail_InvalidFibonacciProof() (gas: 27543)
[PASS] test_ValidFibonacciProof() (gas: 348368)
Suite result: ok. 2 passed; 0 failed; 0 skipped; finished in 7.88ms (7.57ms CPU time)

Ran 1 test suite in 11.28ms (7.88ms CPU time): 2 tests passed, 0 failed, 0 skipped (2 total tests)
test_ValidFibonacciProof() (gas: -3458 (-0.983%))
testFail_InvalidFibonacciProof() (gas: -641 (-2.274%))
Overall gas change: -4099 (-1.079%)

[jtguibas]

Great! Thank you :) We definitely haven't optimized the contract yet.

[jtguibas]

It might sense to merge this PR once we add foundry testing to CI.

[puma314]

We switched to a PLONK prover, which no longer requires this!