After a protocol error (e.g. a malformed line) the read loop ended but
the client still reported IsConnected and later requests waited forever
for a response that could never arrive. The read loop now marks the
connection closed before failing pending requests, and RequestAsync
throws IOException on a closed connection. Adds regression tests and a
raw-line helper to the fake server.
Real loopback TCP socket speaking newline-delimited JSON-RPC 2.0, optionally
TLS with a self-signed certificate, with per-method handlers and call
counters. Lets ElectrumClient, WalletSynchronizer, TransactionInspector, and
CertificatePinStore be exercised against the same code paths used in
production instead of being mocked.
Also exposes UpdateChecker's tag-parsing logic internally so its version
comparison can be tested without a real GitHub API call.
davide