feat(gl-sdk): NodeState snapshot with UTXO-safe balance accounting

[angelix]

Unified node_state() snapshot aggregating get_info, list_peer_channels, and list_funds into a single NodeState record with balances, capacity, utxos, and connected-channel-peer set.

Balance accounting fixes vs. a naive implementation:

• Reserved UTXOs (in-flight PSBTs) are excluded from on-chain balance. FundOutput now carries a reserved field sourced from CLN's listfunds.outputs[].reserved; node_state() skips reserved outputs.
• Closing-channel double-count fixed. Onchain-state channels only contribute to pending_onchain_balance_msat when we initiated the close and our payout is still timelocked (DELAYED_OUTPUT_TO_US), otherwise the payout is already visible as a wallet UTXO and would be counted twice. PeerChannel now exposes closer (ChannelSide) and status to support this gate.
• ChannelState::from_i32 unknown fallback now maps to a new ChannelState::Unknown variant rather than Onchain, which silently counted unmapped states as closing. Unknown is treated as neither open nor closing by balance math.
• Immature outputs (confirmed but timelocked, e.g. coinbase maturation) now surface as their own immature_onchain_balance_msat instead of being silently dropped. OutputStatus match is exhaustive — future variants become a compile error rather than silent zero.
• The three RPCs run concurrently via tokio::join! rather than serially, cutting node_state() latency ~3x on remote nodes.

Mobile-developer API surface:

• id, color, channel_id, peer_id, funding_txid, txid fields use lowercase hex Strings instead of raw Vec, eliminating the encode-for-display step at every call site.
• New aggregate fields: total_onchain_msat (confirmed + unconfirmed + immature), total_balance_msat (everything the user owns), spendable_balance_msat (send-screen gate). All msat for consistency.
• max_chan_reserve_msat (protocol reserve locked across channels).
• utxos: Vec for coin-control UIs. Excludes spent.
• Docstrings on channels_balance_msat / max_payable_msat explicitly name their roles: home-screen display vs send-button gate.
• Docstrings on num_active/pending/inactive_channels clarify which balance fields each count contributes to.
• connected_peers renamed to connected_channel_peers to reflect that it only lists peers we have a channel with; dedup via HashSet.
• fees_collected_msat removed from NodeState (still available on GetInfoResponse); it is a routing-node concern that doesn't belong in the wallet balance snapshot.

Adds ChannelState::is_open and channel_payout_still_pending helpers, NAPI mirror types synced, and refreshes Python + Kotlin NodeState tests to match the new type shape.

[cdecker]

The new channel state Unknown is not covered in a number of match statements, otherwise this is good to go 👍