Refactor runner to use a single instance of Metro for each run (#52777)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/52777

Changelog: [internal]

This significantly speeds up test execution in Fantom (around 2x in OSS and 6x at Meta) by starting a Metro server before all tests runs and reusing it across all tests to build test bundles, instead of spinning up a new Metro instance every time we run each test.

The architecture change (also considering the previous change in buck prebuilds) looks like this:
{F1980689532}

This is how is impacts execution times (compared to the baseline):
* OSS
  * Before: 62s {F1980564286}
  * After: 30s (**2x faster**) {F1980564265}

Reviewed By: andrewdacenko

Differential Revision: D78741903

fbshipit-source-id: b209f88925e49cc2a2067e8df9b7fa9a29b4c8d2