execution: Add scheduler-aware overload to as_sender() for P2300 pipe…

[shivansh023023]

execution: Add scheduler-aware overload to as_sender()

Extends the as_sender() algorithm to accept an optional scheduler parameter,
allowing HPX futures to be adapted into P2300 senders with full scheduler context.

Proposed Changes

• Added as_sender_sender_with_scheduler<Future, Scheduler> template
• Implemented nested env struct following thread_pool_scheduler::sender pattern
• Two specializations for hpx::future<T> and hpx::shared_future<T>
• New two-arg operator() on as_sender_t with C++20 requires constraint
• Scheduler exposed via get_completion_scheduler<set_value_t>()

Enables Pipelines Like

hpx::future<int> f = hpx::async(exec, []{ return 42; });
auto result = stdexec::sync_wait(
    as_sender(std::move(f), get_scheduler(exec))
    | stdexec::then([](int x){ return x * 2; })
);

Context

• Relates to (Re-)Implement executor API on top of sender/receiver infrastructure #5219 (executor modernization for P2300)
• Builds on Implement P2300 get_scheduler bridge for executors #7238, Implement P2300 get_scheduler bridge for parallel_executor #7239 (get_scheduler bridges)
• Follows thread_pool_scheduler::sender::env pattern exactly
• Module compilation verified: ninja hpx_execution passes

Checklist

• I have added a new feature and have added tests to go along with it.

[shivansh023023]

@hkaiser This extends as_sender() with scheduler context preservation,
building on the get_scheduler bridges from #7238/#7239. The implementation
follows thread_pool_scheduler::sender::env pattern

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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[StellarBot]

Can one of the admins verify this patch?

[shivansh023023]

@hkaiser
I have implemented both suggestions
i have Replaced enable_if_t with C++20 requires clause and also deduplicated specializations into single primary template using requires(is_future_v)

[hkaiser]

Besides fixing the reported formatting issues, could you please add tests that scrutinize the new functionalities?

[shivansh023023]

@hkaiser

unit tests added covering Basic construction with scheduler context, Environment querying (get_env, get_completion_scheduler), Full P2300 pipeline integration (schedule | then | sync_wait), shared_future variant (both lvalue and move semantics), void-returning futures, Error propagation through exception channel.

[hkaiser]

@hkaiser

unit tests added covering Basic construction with scheduler context, Environment querying (get_env, get_completion_scheduler), Full P2300 pipeline integration (schedule | then | sync_wait), shared_future variant (both lvalue and move semantics), void-returning futures, Error propagation through exception channel.

Unfortunately your new test fails running.

[hkaiser]

This will break C++20 module compilation. Please use generated module headers only:

Suggested change

	#include <hpx/executors/thread_pool_scheduler.hpp>
	#include <hpx/modules/executors.hpp>