fix(transport-webrtc): detect terminal state at construction time

[paschal533]

Problem

When RTCPeerConnectionMultiaddrConnection is constructed, ICE may have already reached a terminal state ('failed' or 'closed') before the onconnectionstatechange handler is registered. Because that handler is a property assignment, it does not fire retroactively for transitions that already occurred.

This left a half-open connection that the connection manager never cleaned up — the dialing side appeared "connected" while the listening side correctly detected the failure.

Closes #2646

Solution

Explicitly check the initial connectionState at construction time and call onTransportClosed() / peerConnection.close() when the state is already terminal.

Note: 'disconnected' is transient — the ICE agent may recover to 'connected' without intervention — so only 'failed' and 'closed' are treated as terminal here.

Test plan

• Added test: closes immediately when peer connection is already in 'failed' state at construction time
• Added test: closes when peer connection transitions to 'failed' state after construction
• Existing 'can open and close' test still passes

Related PRs

This is one of four focused fixes split from #3406 as requested by @dozyio:

• This PR — initial state check at construction time
• fix(transport-webrtc): fix UnexpectedEOFError race in readCandidatesUntilConnected
• fix(transport-webrtc): do not treat 'disconnected' as a terminal peer connection state
• fix(interface-compliance-tests): increase abort propagation timeout in stream muxer close test