fix(scripting+alarms): close remaining re-review findings

Single commit covering the four small/medium fixes from the updated
code review.

Core.Scripting-014 (Medium, Concurrency):
  CompiledScriptCache.Clear() used the key-only TryRemove(key, out var
  lazy) overload — same race shape Core.Scripting-006 closed in
  GetOrCompile's catch block. A concurrent re-add between snapshot and
  TryRemove was evicted + disposed while the new caller still held it.
  Replaced with the value-scoped TryRemove(KeyValuePair<,>) overload.
  Regression test
  Clear_uses_value_scoped_TryRemove_so_a_race_inserted_entry_survives
  added.

Core.Scripting-013 (Medium, Security):
  Hand-rolled BuildWrapperSource pastes user source between literal
  braces; brace-balanced source could inject sibling methods/classes
  alongside CompiledScript.Run. Analyzer still walked the injected
  members so it wasn't a direct escape, but it relaxed the documented
  'method body' authoring contract. Added EnforceSingleRunMember:
  after ParseText, the compilation unit must hold exactly one type
  (CompiledScript) and that type must hold exactly one member (the Run
  method). Any deviation throws CompilationErrorException with LMX001/
  LMX002 diagnostic IDs and a Core.Scripting-013 reference in the
  message. Two regression tests added covering the sibling-method and
  sibling-class injection vectors.

Core.Scripting-015 (Low, Correctness, latent):
  ToCSharpTypeName's generic branch truncated at the first backtick via
  IndexOf, silently dropping closed args of nested-generic shapes
  (Outer<T>.Inner<U>). No production caller exercises this shape today
  (all TContext/TResult are top-level non-nested), so the bug was
  latent. Rewrote the generic branch to walk the FullName segment-by-
  segment, consuming generic args per segment so nested shapes emit
  valid C# (global::Ns.Outer<T>.Inner<U> rather than the broken
  Outer<T,U>).

Core.ScriptedAlarms-013 (Low, Documentation):
  The internal test accessors TryGetScratchReadCacheForTest /
  TryGetScratchContextForTest return live mutable scratch refilled in
  place under _evalGate. XML docs didn't warn future test authors about
  the synchronization contract. Added a <remarks> block to each
  documenting the only-safe-on-quiesced-engine + identity-or-single-key
  contract.

Verification (suites green):
  Core.Scripting.Tests: 110/110 (was 107 — +3 new rejection/race tests)
  Core.ScriptedAlarms.Tests: 67/67 (unchanged — doc-only fix)
  Core.VirtualTags.Tests: 57/57 (unchanged)

After this commit, all 12 findings from the updated re-review are
closed (10 Resolved, 1 Won't Fix none, 1 Deferred — Driver.Galaxy-017).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/Core/ZB.MOM.WW.OtOpcUa.Core.Scripting/CompiledScriptCache.cs

@@ -99,14 +99,19 @@ public sealed class CompiledScriptCache<TContext, TResult> : IDisposable
     /// </remarks>
     public void Clear()
     {
-        // Snapshot the entries, swap them out, then dispose. We use TryRemove rather
-        // than _cache.Clear() so a concurrent GetOrCompile re-add after our snapshot
-        // is not silently lost — a new compile starts a fresh cache entry, the old
-        // evaluator is still disposed.
-        foreach (var key in _cache.Keys.ToArray())
+        // Snapshot (key, value) pairs and remove with the value-scoped
+        // TryRemove(KeyValuePair<,>) overload — same shape as the
+        // Core.Scripting-006 fix in GetOrCompile's catch block. A concurrent
+        // GetOrCompile re-add that hashes to the same key between our snapshot
+        // and the TryRemove inserts a *different* Lazy reference; the value-
+        // scoped removal sees the mismatch and leaves the fresh entry intact
+        // (instead of evicting + disposing it while the concurrent caller
+        // still holds it). The fresh evaluator and its ALC stay live for the
+        // concurrent caller. (Core.Scripting-014.)
+        foreach (var entry in _cache.ToArray())
         {
-            if (_cache.TryRemove(key, out var lazy))
-                DisposeLazyIfMaterialised(lazy);
+            if (_cache.TryRemove(entry))
+                DisposeLazyIfMaterialised(entry.Value);
         }
     }