fix: update simplecov to 1.0.0

[xuan-cao-swi]

From crmne/ruby_llm#842

SimpleCov.running accessor that existed in 0.22.x. It was undocumented/internal API, so its removal isn't in the breaking-changes list — but the wrapper depends on it.

Remove the check if SimpleCov.running

[thompson-tomo]

@xuan-cao-swi another solution is in open-telemetry/opentelemetry-ruby#2117 key thing is the finalize option.

[xuan-cao-swi]

SimpleCov::ResultMerger.store_result is required because the tests run across multiple processes and each process generates its own isolated coverage report.

[thompson-tomo]

That is exactly what finalizing is for https://github.com/simplecov-ruby/simplecov#merge-finalization-ownership which even shows the forking example