Deduplicate iwant list

[twoeths]

Motivation
Right now if n peers sending the same message that we don't have, we'll ask for the same message to these n peers

• If we receive N IHAVE for a msgId, we will send N IWANT for that msgId
• We want to deduplicate this
• This should also help us get more messages that we don't have

Description
Track pendingIWant and clear per heartbeat as referenced in https://github.com/libp2p/rust-libp2p/blob/802d00e645894d8895f2f9f665b921452d992b86/protocols/gossipsub/src/behaviour.rs#L1223

[stale]

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