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/S7/S7_1500SmokeTests.cs

@@ -25,6 +25,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests.S7;
 public sealed class S7_1500SmokeTests(ModbusSimulatorFixture sim)
 {
     /// <summary>Verifies that an S7-1500 roundtrip write then read of a holding register succeeds.</summary>
+    /// <returns>A task that represents the asynchronous test.</returns>
     [Fact]
     public async Task S7_1500_roundtrip_write_then_read_of_holding_register()
     {

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/S7/S7_ByteOrderTests.cs

@@ -17,6 +17,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests.S7;
 public sealed class S7_ByteOrderTests(ModbusSimulatorFixture sim)
 {
     /// <summary>Verifies that S7 Float32 with ABCD byte order correctly decodes 1.5f from HR100.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task S7_Float32_ABCD_decodes_1_5f_from_HR100()
     {
@@ -63,6 +64,7 @@ public sealed class S7_ByteOrderTests(ModbusSimulatorFixture sim)
     }
 
     /// <summary>Verifies that S7 Int32 with ABCD byte order correctly decodes 0x12345678 from HR300.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task S7_Int32_ABCD_decodes_0x12345678_from_HR300()
     {
@@ -98,6 +100,7 @@ public sealed class S7_ByteOrderTests(ModbusSimulatorFixture sim)
     }
 
     /// <summary>Verifies that S7 DB1 fingerprint marker reads 0xABCD from HR0.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task S7_DB1_fingerprint_marker_at_HR0_reads_0xABCD()
     {