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.Modbus.IntegrationTests/AddressingGrammarTests.cs

@@ -36,6 +36,7 @@ public sealed class AddressingGrammarTests
     }
 
     /// <summary>Verifies that 5-digit and 6-digit Modicon formats map to the same wire offset.</summary>
+    /// <returns>A task that represents the asynchronous test operation.</returns>
     [Fact]
     public async Task Modicon_5_And_6_Digit_Both_Map_To_Same_Wire_Offset()
     {
@@ -54,6 +55,7 @@ public sealed class AddressingGrammarTests
     }
 
     /// <summary>Verifies that Float32 values roundtrip correctly with CDAB byte order.</summary>
+    /// <returns>A task that represents the asynchronous test operation.</returns>
     [Fact]
     public async Task Float32_With_CDAB_Roundtrips_Through_Wire()
     {
@@ -76,6 +78,7 @@ public sealed class AddressingGrammarTests
     }
 
     /// <summary>Verifies that Int16 array reads surface as typed arrays.</summary>
+    /// <returns>A task that represents the asynchronous test operation.</returns>
     [Fact]
     public async Task Int16_Array_Reads_Surface_As_Typed_Array()
     {
@@ -93,6 +96,7 @@ public sealed class AddressingGrammarTests
     }
 
     /// <summary>Verifies that block read coalescing reduces PDU count end-to-end.</summary>
+    /// <returns>A task that represents the asynchronous test operation.</returns>
     [Fact]
     public async Task Block_Read_Coalescing_Reduces_PDU_Count_End_To_End()
     {