t8n produces truncated trace

[chfast]

For an execution with a very long trace, the trace output file of evmone-t8n --trace may be truncated.

Some example tests with very long trace can be found in https://github.com/ethereum/execution-spec-tests/pull/1591.

With EEST's fill you can generate evmone-t8n invocation. Add --trace to the t8n.sh.

The bug may be related to stream buffering. We are redirecting standard output to a file with https://github.com/ethereum/evmone/blob/master/test/t8n/t8n.cpp#L169-L181. Maybe we need to properly close it?

Reported by @danceratopz.