eof: Return constant hash of EXTCODEHASH of EOF

[chfast]

Replace runtime evaluated keccak256("EF00") with a constant returned for an account with EOF code.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 94.21%. Comparing base (2cd8bf7) to head (02b6951). Report is 3 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1035 +/- ## ======================================= Coverage 94.21% 94.21% ======================================= Files 153 153 Lines 15927 15933 +6 ======================================= + Hits 15005 15011 +6 Misses 922 922 ``` | [Flag](https://app.codecov.io/gh/ethereum/evmone/pull/1035/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum) | Coverage Δ | | |---|---|---| | [eof_execution_spec_tests](https://app.codecov.io/gh/ethereum/evmone/pull/1035/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum) | `17.53% <75.00%> (+0.01%)` | :arrow_up: | | [ethereum_tests](https://app.codecov.io/gh/ethereum/evmone/pull/1035/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum) | `27.34% <66.66%> (+<0.01%)` | :arrow_up: | | [ethereum_tests_silkpre](https://app.codecov.io/gh/ethereum/evmone/pull/1035/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum) | `19.15% <45.45%> (+0.01%)` | :arrow_up: | | [execution_spec_tests](https://app.codecov.io/gh/ethereum/evmone/pull/1035/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum) | `20.45% <41.66%> (+0.01%)` | :arrow_up: | | [unittests](https://app.codecov.io/gh/ethereum/evmone/pull/1035/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum) | `89.00% <91.66%> (-0.01%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum#carryforward-flags-in-the-pull-request-comment) to find out more. | [Files with missing lines](https://app.codecov.io/gh/ethereum/evmone/pull/1035?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum) | Coverage Δ | | |---|---|---| | [lib/evmone/eof.cpp](https://app.codecov.io/gh/ethereum/evmone/pull/1035?src=pr&el=tree&filepath=lib%2Fevmone%2Feof.cpp&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum#diff-bGliL2V2bW9uZS9lb2YuY3Bw) | `85.68% <100.00%> (ø)` | | | [lib/evmone/eof.hpp](https://app.codecov.io/gh/ethereum/evmone/pull/1035?src=pr&el=tree&filepath=lib%2Fevmone%2Feof.hpp&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum#diff-bGliL2V2bW9uZS9lb2YuaHBw) | `100.00% <ø> (ø)` | | | [test/state/host.cpp](https://app.codecov.io/gh/ethereum/evmone/pull/1035?src=pr&el=tree&filepath=test%2Fstate%2Fhost.cpp&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum#diff-dGVzdC9zdGF0ZS9ob3N0LmNwcA==) | `100.00% <100.00%> (ø)` | | | [test/unittests/eof\_test.cpp](https://app.codecov.io/gh/ethereum/evmone/pull/1035?src=pr&el=tree&filepath=test%2Funittests%2Feof_test.cpp&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum#diff-dGVzdC91bml0dGVzdHMvZW9mX3Rlc3QuY3Bw) | `94.00% <100.00%> (+0.25%)` | :arrow_up: |