Expose Test Reset Function

[svozza]

Our library can run both inside and outisde the InvokeStore async context. As such, I have suites of concurrency tests to verify theconcurrency behiours I expect to see. After the change in v0.2.x to change the instantiation logic, ie., the introduction of getInstanceAsync this has made testing much more difficult.

This is because the new _testing field is only added if the AWS_LAMBDA_BENCHMARK_MODE is set to 1 at the very first time the module is imported. This means that if InvokeStore is imported at the top level anywhere before your test, i.e., in application code, then the _testing.reset function will not be there. Using vi.strubEnv in a before block will not work because it is too late, the module has long been imported before then.

I propose that this reset function should always be available without the need for AWS_LAMBDA_BENCHMARK_MODE to allow for ease of testing for codebases that need to support both environments where InvokeStore needs to be use to manage async contexts and where it does not