[Darwin] Address gemini-code-assist review feedback on PR project-chip#72211

Two fixes per project-chip#72211 review:

* MTRDeviceAttestationDelegateBridge.mm: switch the attestationUserInfo
  construction from an NSDictionary literal to a mutable dictionary with nil
  checks. NSDictionary literal syntax @{key:value} raises
  NSInvalidArgumentException on a nil value; the @(uint16_t) boxing for the
  VID/PID NSNumbers always succeeds today, but defensive construction guards
  against future DeviceInfoForAttestation struct changes that could make those
  fields nullable.

* MTRError.mm: handle Windows-style backslash path separators in
  errorCode.GetFile() basename stripping. CHIP builds run on Windows for some
  embedded controller targets; without the fallback to strrchr(file, '\\'),
  full Windows build-host paths would land in MTRCHIPErrorSourceFileKey,
  defeating the privacy intent.

Both flagged by gemini-code-assist's automated review.

Author: woody-apple

src/darwin/Framework/CHIP/MTRDeviceAttestationDelegateBridge.mm

@@ -78,11 +78,19 @@
         // certified vendor / product IDs from BasicInformation cluster — partner already
         // knows their own VID/PID, but presence in userInfo lets triage tooling correlate
         // attestation failures by device-class without parsing logs.
-        NSDictionary<NSErrorUserInfoKey, id> * attestationUserInfo = @{
-            MTRAttestationVerificationResultKey : @(chip::to_underlying(attestationResult)),
-            MTRAttestationDeviceVendorIDKey : basicInformationVendorID,
-            MTRAttestationDeviceProductIDKey : basicInformationProductID,
-        };
+        //
+        // Use a mutable dictionary with nil checks rather than an NS dictionary literal:
+        // `@{ key : value }` raises NSInvalidArgumentException if any value is nil. The VID/PID
+        // NSNumbers are non-nil today (the @(uint16_t) boxing always succeeds), but defensive
+        // construction guards against future struct changes that make those fields nullable.
+        NSMutableDictionary<NSErrorUserInfoKey, id> * attestationUserInfo = [NSMutableDictionary dictionary];
+        attestationUserInfo[MTRAttestationVerificationResultKey] = @(chip::to_underlying(attestationResult));
+        if (basicInformationVendorID != nil) {
+            attestationUserInfo[MTRAttestationDeviceVendorIDKey] = basicInformationVendorID;
+        }
+        if (basicInformationProductID != nil) {
+            attestationUserInfo[MTRAttestationDeviceProductIDKey] = basicInformationProductID;
+        }
 
         id<MTRDeviceAttestationDelegate> strongDelegate = mDeviceAttestationDelegate;
         if ([strongDelegate respondsToSelector:@selector(deviceAttestationCompletedForController:opaqueDeviceHandle:attestationDeviceInfo:error:)]

src/darwin/Framework/CHIP/MTRError.mm

@@ -167,10 +167,15 @@ + (NSError *)errorForCHIPErrorCode:(CHIP_ERROR)errorCode
 
     // Surface CHIP source-file basename + line when CHIP was built with
     // CHIP_CONFIG_ERROR_SOURCE. The full path is intentionally elided to avoid
-    // exposing build-host paths; only the basename is forwarded.
+    // exposing build-host paths; only the basename is forwarded. Check both
+    // forward and backward slashes so basename-stripping works on Windows builds
+    // as well as Unix-style hosts.
     const char * sourceFile = errorCode.GetFile();
     if (sourceFile != nullptr && sourceFile[0] != '\0') {
         const char * basename = strrchr(sourceFile, '/');
+        if (basename == nullptr) {
+            basename = strrchr(sourceFile, '\\');
+        }
         userInfo[MTRCHIPErrorSourceFileKey] = @((basename != nullptr) ? basename + 1 : sourceFile);
         userInfo[MTRCHIPErrorSourceLineKey] = @(errorCode.GetLine());
     }