v0.17.2

0.17.1 reached PyPI and the GitHub release but never reached crates.io: the
publish gate ran the workspace test suite and one test failed on the runner.
This release carries the same contents as 0.17.1 plus the fix, and is the
version to use. Crate versions: nanobook 0.17.2, nanobook-broker 0.8.1,
nanobook-risk 0.6.4, nanobook-rebalancer 0.8.4.

Changed

• MSRV raised from 1.86 to 1.88 across all four crates. The 1.86 claim was
  already false for nanobook-broker, nanobook-risk and
  nanobook-rebalancer: the 0.17.1 dependency sweep pulled time to 0.3.54
  (via ibapi and tracing-appender), which requires 1.88. Declaring 1.88
  everywhere keeps one number across the workspace. Cargo's resolver is
  MSRV-aware, so a consumer on an older toolchain resolves to an earlier
  version rather than failing to build.
• Nested if let blocks in level, price_levels, stop, exchange,
  backtest_bridge and two examples are now let-chains, which 1.88 permits.
  Machine-applied and semantically identical; the suite is unchanged at 1134
  passing.

Fixed

• nanobook-rebalancer did not compile on Windows. The #[cfg(windows)]
  arm of the kill switch opened with use windows::Win32::System::Console::…
  for symbols it never referenced, and the windows crate was never declared
  as a dependency. The import is removed; the arm already returned "Kill
  switch not fully supported on Windows yet" unconditionally, so behaviour is
  unchanged. Every published version of this crate has been broken on Windows.
• test_reconciliation_blocks_submission no longer calls the live Binance
  API. It opened a real connection as setup, so it failed with
  451 Unavailable For Legal Reasons on runners in regions Binance
  restricts. submit_order checks the reconciliation flag before it requires
  a client, so the connection was never needed for the assertion; the test
  still fails if that check order is ever reversed.
• CI ran cargo test --all-features without --workspace, so it only
  ever tested the root crate — the broker, risk and rebalancer suites were
  invisible to it apart from three explicitly-named failure-injection drills.
  That is why a test making live network calls survived unnoticed. The test
  job now runs the whole workspace.