review(Driver.AbLegacy): fix Bit write 1-byte/2-byte encode-decode mismatch (Medium)

Re-review at 7286d320. -014 (Medium): Bit EncodeValue (no bitIndex) wrote SetInt8 while
DecodeValue read GetInt16 on a 16-bit B-file element, so a false write could round-trip
as true (stale high byte). Fix: SetInt16 + TDD. -015: tests pass CancellationToken.

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/AbLegacyCapabilityTests.cs

@@ -89,7 +89,7 @@ public sealed class AbLegacyCapabilityTests
 
         var afterUnsub = events.Count;
         tagRef.Value = 999;
-        await Task.Delay(300);
+        await Task.Delay(300, TestContext.Current.CancellationToken);
         events.Count.ShouldBe(afterUnsub);
     }
 
@@ -171,7 +171,7 @@ public sealed class AbLegacyCapabilityTests
             Probe = new AbLegacyProbeOptions { Enabled = true, ProbeAddress = null },
         }, "drv-1");
         await drv.InitializeAsync("{}", CancellationToken.None);
-        await Task.Delay(200);
+        await Task.Delay(200, TestContext.Current.CancellationToken);
 
         drv.GetHostStatuses().Single().State.ShouldBe(HostState.Unknown);
         await drv.ShutdownAsync(CancellationToken.None);