docs: complete XML doc comments via fixdocs (2757 to 131 findings)

Add missing <returns>/<param>/<summary>/<typeparam> tags and clean up
misused inheritdoc across 481 files so the documented API surface is
complete. Documentation-only (zero code lines changed). The 131 remaining
findings are inheritdoc-style warnings deliberately left to preserve
hand-written implementation rationale (plan-decision notes, race-condition
explanations).

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/AbCipSubscriptionTests.cs

@@ -21,6 +21,7 @@ public sealed class AbCipSubscriptionTests
     }
 
     /// <summary>Verifies that the initial poll raises OnDataChange events for every subscribed tag.</summary>
+    /// <returns>A task that represents the asynchronous test.</returns>
     [Fact]
     public async Task Initial_poll_raises_OnDataChange_for_every_tag()
     {
@@ -47,6 +48,7 @@ public sealed class AbCipSubscriptionTests
     }
 
     /// <summary>Verifies that unchanged values raise OnDataChange only once (on initial poll).</summary>
+    /// <returns>A task that represents the asynchronous test.</returns>
     [Fact]
     public async Task Unchanged_value_raises_only_once()
     {
@@ -66,6 +68,7 @@ public sealed class AbCipSubscriptionTests
     }
 
     /// <summary>Verifies that value changes between polls raise OnDataChange events.</summary>
+    /// <returns>A task that represents the asynchronous test.</returns>
     [Fact]
     public async Task Value_change_between_polls_raises_OnDataChange()
     {
@@ -89,6 +92,7 @@ public sealed class AbCipSubscriptionTests
     }
 
     /// <summary>Verifies that unsubscribe halts polling and no further events are raised.</summary>
+    /// <returns>A task that represents the asynchronous test.</returns>
     [Fact]
     public async Task Unsubscribe_halts_polling()
     {
@@ -112,6 +116,7 @@ public sealed class AbCipSubscriptionTests
     }
 
     /// <summary>Verifies that polling intervals below 100ms are floored to the minimum.</summary>
+    /// <returns>A task that represents the asynchronous test.</returns>
     [Fact]
     public async Task Interval_below_100ms_is_floored()
     {
@@ -133,6 +138,7 @@ public sealed class AbCipSubscriptionTests
     }
 
     /// <summary>Verifies that ShutdownAsync cancels all active subscriptions.</summary>
+    /// <returns>A task that represents the asynchronous test.</returns>
     [Fact]
     public async Task ShutdownAsync_cancels_active_subscriptions()
     {
@@ -154,6 +160,7 @@ public sealed class AbCipSubscriptionTests
     }
 
     /// <summary>Verifies that subscriptions on UDT members use the synthesized full reference.</summary>
+    /// <returns>A task that represents the asynchronous test.</returns>
     [Fact]
     public async Task Subscription_on_UDT_member_uses_synthesised_full_reference()
     {