sdk(local_relay): add LocalRelay::connections_left - #1459

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, actions/github-script@60a0d83039c74a4aee543508d2ffcb1c3799cdea, Swatinem/rust-cache@v2.7.8. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

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