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.AbLegacy.IntegrationTests/AbLegacyReadSmokeTests.cs

@@ -37,6 +37,7 @@ public sealed class AbLegacyReadSmokeTests(AbLegacyServerFixture sim)
 
     /// <summary>Verifies that the driver reads seeded N file from the AB server via PCCC.</summary>
     /// <param name="profile">The AB Legacy server profile describing the fixture endpoint.</param>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [AbLegacyTheory]
     [MemberData(nameof(Profiles))]
     public async Task Driver_reads_seeded_N_file_from_ab_server_PCCC(AbLegacyServerProfile profile)
@@ -73,6 +74,7 @@ public sealed class AbLegacyReadSmokeTests(AbLegacyServerFixture sim)
     }
 
     /// <summary>Verifies that SLC500 write-then-read round trip succeeds on N7 scratch register.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [AbLegacyFact]
     public async Task Slc500_write_then_read_round_trip_on_N7_scratch_register()
     {