test(raft): cold-node rejoin and wiped-node join e2e

Includes two raft fixes the e2e exposed:
- heartbeatLoop drops cached peer sockets on leadership acquisition
  (half-dead sockets to a restarted peer never errored, so no redial
  ever happened and the cluster livelocked without heartbeats)
- restoreSnapshot repoints tcpServer ctx/db at the reopened database
  (queries kept reading the closed pre-restore LSM, serving 0 rows)

.github/workflows/ci.yml

@@ -83,6 +83,7 @@ jobs:
           nim c -d:ssl --threads:on --path:src -r tests/raft_writes_e2e_test.nim
           nim c -d:ssl --threads:on --path:src -r tests/raft_failover_load_e2e_test.nim
           nim c -d:ssl --threads:on --path:src -r tests/raft_tls_e2e_test.nim
+          nim c -d:ssl --threads:on --path:src -r tests/raft_coldnode_e2e_test.nim
 
   verify:
     runs-on: ubuntu-latest