test(forms): improve test coverage for multiple pattern validators

Add comprehensive test cases to validate behavior when multiple
pattern validators are applied to the same field.

These tests clarify that multiple patterns operate with AND logic,
where each pattern is validated independently and produces its own
error when it doesn't match.

(cherry picked from commit 7fd076bdd3)

packages/forms/signals/test/node/api/validators/pattern.spec.ts

@@ -95,6 +95,57 @@ describe('pattern validator', () => {
       expect(f.name().pattern()).toEqual([/pir.*jok/, /pelmeni/]);
     });
 
+    it('validates multiple patterns independently (AND logic)', () => {
+      const model = signal('abc123');
+      const f = form(
+        model,
+        (p) => {
+          pattern(p, /abc/); // matches
+          pattern(p, /\d+/); // matches
+        },
+        {injector: TestBed.inject(Injector)},
+      );
+
+      // Both patterns match, so no errors
+      expect(f().pattern()).toEqual([/abc/, /\d+/]);
+      expect(f().errors()).toEqual([]);
+    });
+
+    it('validates multiple patterns independently - partial match produces errors', () => {
+      const model = signal('abc');
+      const f = form(
+        model,
+        (p) => {
+          pattern(p, /abc/); // matches
+          pattern(p, /\d+/); // does not match
+        },
+        {injector: TestBed.inject(Injector)},
+      );
+
+      // Only one pattern matches, so we get an error from the non-matching one
+      expect(f().pattern()).toEqual([/abc/, /\d+/]);
+      expect(f().errors()).toEqual([patternError(/\d+/, {fieldTree: f})]);
+    });
+
+    it('validates multiple patterns - no match produces multiple errors', () => {
+      const model = signal('xyz');
+      const f = form(
+        model,
+        (p) => {
+          pattern(p, /abc/); // does not match
+          pattern(p, /\d+/); // does not match
+        },
+        {injector: TestBed.inject(Injector)},
+      );
+
+      // No patterns match, so we get errors from both
+      expect(f().pattern()).toEqual([/abc/, /\d+/]);
+      expect(f().errors()).toEqual([
+        patternError(/abc/, {fieldTree: f}),
+        patternError(/\d+/, {fieldTree: f}),
+      ]);
+    });
+
     it('PATTERN property defaults to empty list', () => {
       const cat = signal({name: 'pelmeni-the-cat'});
       const f = form(