fix: release peer lock before persistence

[ovitrif]

Summary

Android production ANRs in synonymdev/bitkit-android#1036 show Node::list_peers blocked while acquiring PeerStore.peers.read().

PeerStore::add_peer and PeerStore::remove_peer currently retain peers.write() while persisting the updated peer set. With VssStore, the synchronous KVStoreSync::write bridges remote persistence through block_in_place and internal_runtime.block_on. A slow remote write therefore retains the peer-store write lock for network duration and blocks every synchronous list_peers reader.

Symbolicated production stack

The affected Bitkit v2.3.0 build 182 uses ldk-node-android:0.7.0-rc.46 from source commit 3ace915250296cbbc3069b2c23030d2cdf7ba834.

The released Bitkit APK, rc.46 Maven AAR, and committed rc.46 Android library contain the same arm64 ELF:

• size: 14,213,792 bytes
• SHA-256: fbb450b145054f0682d966c5326cf88a477c9efd1c82b3c74e70d0bb7acabc48
• .text: 0x561280..0xd338d0

The Play program counters are direct ELF VMAs. The exported uniffi_ldk_node_fn_method_node_list_peers symbol starts at 0x963f88; Play frame 0x963fc4 is +60 inside that function.

#00 bionic syscall
#01 0xcfa090 std futex wait / RwLock read contention
#02 0x661c5c std::sys::sync::rwlock::futex::RwLock::read_contended
#03 0x791a90 ldk_node::peer_store::PeerStore::list_peers
#04 0x79ba58 ldk_node::Node::list_peers
#05 0x60cfe8 UniFFI scaffolding for Node::list_peers
#06 0x619894 UniFFI callback wrapper for Node::list_peers
#07 0x963fc4 uniffi_ldk_node_fn_method_node_list_peers + 60

Source attribution:

• src/peer_store.rs:44-72: add_peer and remove_peer retain self.peers.write() across persist_peers
• src/peer_store.rs:74-75: list_peers acquires self.peers.read()
• src/peer_store.rs:82-102: persist_peers calls KVStoreSync::write
• src/io/vss_store.rs:191-219: VssStore::write waits for remote persistence through block_in_place and internal_runtime.block_on

The same lock scope remains on current fork main at a94255c88dff1c723fc1741dc52a5b4f664cb95f.

Required behavior

• Serialize peer mutations independently from peer snapshot reads.
• Restrict the peer RwLock to the in-memory mutation and snapshot.
• Complete storage I/O after releasing the peer RwLock.
• Preserve persistence failure and retry semantics.
• Add a concurrent regression test whose fake KVStoreSync::write remains blocked while list_peers returns promptly.
• Bump the crate version, regenerate mobile bindings, and publish a release for Android and iOS consumption.

Upstream lightningdevkit#919 implemented this lock-scope pattern in commit d49b681.