stdcoroutine-3: Migrate coroutine tests from Boost.Coroutine to C++20 coroutines

[pratikmankawde]

High Level Overview of Change

Rewrite Coroutine_test.cpp and JobQueue_test.cpp to use postCoroTask() and co_await runner->suspend() instead of the old postCoro() / Coro::yield() API. After this change, zero .cpp files reference postCoro() or JobQueue::Coro.

Context of Change

This is Milestone 3 of the Boost.Coroutine → C++20 coroutines migration. Milestone 2 (pratik/std-coro/migrate-entry-points) migrated all production entry points. This milestone completes the migration of the last remaining callers — the test files.

• Milestone 1 (pratik/std-coro/add-coroutine-primitives): Added CoroTask<T>, CoroTaskRunner, JobQueueAwaiter, postCoroTask()
• Milestone 2 (pratik/std-coro/migrate-entry-points): Migrated all production entry points
• Milestone 3 (pratik/std-coro/migrate-test-code): Migrated all test code
• Milestone 4 (this PR): Delete old code and build dependencies

Coroutine_test (3 tests):

• correct_order: postCoro → postCoroTask, yield() → co_await runner->suspend()
• incorrect_order: Same migration. The post()-before-suspend() pattern remains safe because CoroTaskRunner::mutex_ serializes resume calls — the posted job's resume() blocks until the current resume() releases the lock after the coroutine suspends.
• thread_specific_storage: shared_ptr<Coro> → shared_ptr<CoroTaskRunner>, same suspend/resume pattern.

JobQueue_test (testPostCoro → testPostCoroTask, 3 sub-tests):

• Repeated post() until completion
• Repeated resume() (synchronous) until completion
• Shutdown rejection (postCoroTask returns nullptr)

Type of Change

• Refactor (non-breaking change that only restructures code)
• Tests (you added tests for code that already exists, or your new feature included in this PR)

API Impact

• libxrpl change (any change that may affect libxrpl or dependents of libxrpl)

Future Tasks

• Milestone 4: Delete Coro.ipp, remove old Coro class and postCoro() from JobQueue.h, remove Boost.Coroutine from CMake/Conan dependencies

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (pratik/std-coro/migrate-entry-points@bdd3659). Learn more about missing BASE report.

Additional details and impacted files

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