feat: add scheduler support for timeout management in Multiselect

[kamilsa]

Adds timeout on MultiselectInstance's selectOneOf

[Copilot]

Pull Request Overview

This PR adds scheduler support for timeout management in the Multiselect module to ensure that protocol negotiations do not hang indefinitely.

• Introduces a timeout for negotiations in MultiselectInstance using a scheduler.
• Updates the Multiselect and header files to pass and store the scheduler pointer.
• Adds an onTimeout handler that closes the connection upon timeout.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/protocol_muxer/multiselect/multiselect_instance.cpp	Adds scheduler-based timeout scheduling and corresponding cancellation in close().
src/protocol_muxer/multiselect.cpp	Passes scheduler pointer when creating a new MultiselectInstance.
include/libp2p/protocol_muxer/multiselect/multiselect_instance.hpp	Declares the scheduler member, timeout handle, and onTimeout() method.
include/libp2p/protocol_muxer/multiselect.hpp	Introduces the scheduler pointer as part of the Multiselect class.

[turuslan]

Should we reset() connection/stream, to cancel pending read/write?

[kamilsa]

I think it will be automatically reset, once we erase this active instance:

cpp-libp2p/src/protocol_muxer/multiselect.cpp

Lines 56 to 64 in 4bd3a78

	void Multiselect::instanceClosed(Instance instance,
	const ProtocolHandlerFunc &cb,
	outcome::result<peer::ProtocolName> result) {
	active_instances_.erase(instance);
	if (cache_.size() < kMaxCacheSize) {
	cache_.emplace_back(std::move(instance));
	}
	cb(std::move(result));
	}

It might live a little longer in the cache, but eventually a new connection will replace the one from the instance