Standarized spector scenario generator

On top of having a combined conifg https://github.com/Azure/typespec-azure/issues/4997 we might be able to share the logic for generating the spector tests, this would reduce the eng maintenance of each team and improve contributor/agent experience not having to find many ways to deal with things.
It probably also can be implemented in a more preformant way than all of them right now bringing perf benefit for everyone.

Things to take into account
- might need specific option support for a scenario https://github.com/microsoft/typespec/blob/main/packages/http-client-python/eng/scripts/ci/regenerate-common.ts#L84

Start with the combined config issue #4997 and inspect the referenced regenerate-common.ts location around line 84 for scenario-specific options. Compare the existing Spector test generation approaches, define the shared scope and option support, and verify that teams can use the standardized generator with reduced maintenance and improved performance.

Written by the indexing model from the issue text.