test: Improve out-of-buffer detection in EOF tests

[chfast]

In EOF validation tests, move the container to new heap-allocated buffer of exact size to easily find out-of-buffer reads with address sanitizer.

[codecov[bot]]

Codecov Report

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

Project coverage is 94.30%. Comparing base (26d5609) to head (6a792b3).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #958 +/- ## ======================================= Coverage 94.29% 94.30% ======================================= Files 143 143 Lines 16138 16142 +4 ======================================= + Hits 15218 15222 +4 Misses 920 920 ``` | [Flag](https://app.codecov.io/gh/ethereum/evmone/pull/958/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/958/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum) | `16.93% <0.00%> (-0.01%)` | :arrow_down: | | [ethereum_tests](https://app.codecov.io/gh/ethereum/evmone/pull/958/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum) | `26.90% <0.00%> (-0.01%)` | :arrow_down: | | [ethereum_tests_silkpre](https://app.codecov.io/gh/ethereum/evmone/pull/958/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum) | `18.68% <0.00%> (-0.01%)` | :arrow_down: | | [execution_spec_tests](https://app.codecov.io/gh/ethereum/evmone/pull/958/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum) | `17.90% <0.00%> (-0.01%)` | :arrow_down: | | [unittests](https://app.codecov.io/gh/ethereum/evmone/pull/958/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum) | `89.73% <100.00%> (+<0.01%)` | :arrow_up: | 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](https://app.codecov.io/gh/ethereum/evmone/pull/958?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum) | Coverage Δ | | |---|---|---| | [test/unittests/eof\_validation.cpp](https://app.codecov.io/gh/ethereum/evmone/pull/958?src=pr&el=tree&filepath=test%2Funittests%2Feof_validation.cpp&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ethereum#diff-dGVzdC91bml0dGVzdHMvZW9mX3ZhbGlkYXRpb24uY3Bw) | `93.22% <100.00%> (+0.23%)` | :arrow_up: |