refactor(driver-s7): extract S7DriverOptions to .Contracts with parallel CpuType enum

Introduces Driver.S7.Contracts (dependency-free POCO project) and moves
S7DriverOptions / S7ProbeOptions / S7TagDefinition / S7DataType into it.
Adds S7CpuType enum mirroring S7.Net.CpuType exactly (7 values with
explicit integer codes). Runtime S7CpuTypeMap bridges S7CpuType →
S7.Net.CpuType at the single Plc construction site in S7Driver.InitializeAsync.
S7DriverFactoryExtensions and S7CommandBase updated to use S7CpuType; test
files updated to match (S7_1500Profile, S7DriverScaffoldTests). AdminUI can
now reference Driver.S7.Contracts without pulling in S7netplus.

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7.IntegrationTests/S7_1500/S7_1500Profile.cs

@@ -1,5 +1,3 @@
-using S7NetCpuType = global::S7.Net.CpuType;
-
 namespace ZB.MOM.WW.OtOpcUa.Driver.S7.IntegrationTests.S7_1500;
 
 /// <summary>
@@ -34,7 +32,7 @@ public static class S7_1500Profile
     {
         Host = host,
         Port = port,
-        CpuType = S7NetCpuType.S71500,
+        CpuType = S7CpuType.S71500,
         Rack = 0,
         Slot = 0,
         Timeout = TimeSpan.FromSeconds(5),

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7.Tests/S7DriverScaffoldTests.cs

@@ -18,7 +18,7 @@ public sealed class S7DriverScaffoldTests
     {
         var opts = new S7DriverOptions();
         opts.Port.ShouldBe(102, "ISO-on-TCP is always 102 for S7; documented in driver-specs.md §5");
-        opts.CpuType.ShouldBe(global::S7.Net.CpuType.S71500);
+        opts.CpuType.ShouldBe(S7CpuType.S71500);
         opts.Rack.ShouldBe((short)0);
         opts.Slot.ShouldBe((short)0, "S7-1200/1500 onboard PN ports are slot 0 by convention");
     }