test(control-plane): separate orchestration tests from EC2 provider tests (github-aws-runners#5246)

## Description

- Move generic scale-up and scale-down orchestration tests from the EC2
provider package into the control-plane package.
- Test orchestration through the runner-provider interfaces and
registry.
- Keep EC2 resource operations and dynamic configuration coverage beside
the EC2 provider.
- Remove direct EC2 provider test imports and mocks of control-plane
modules.

Production behavior is unchanged.

## Test Plan

- `cd lambdas && yarn test` (all 8 projects passed)
- Focused control-plane suites: 226 tests passed
- Focused EC2 provider suites: 158 tests passed
- ESLint and Prettier checks passed for control-plane and
runner-providers
- Exact test-title inventory: 276 before and after, with no additions or
removals
- `git diff --check`

## Related Issues

Closes github-aws-runners#5236

Follow-up to github-aws-runners#5234

Author: edersonbrilhante