[text] Store pattern as const char* to reduce memory usage

tests/integration/fixtures/api_message_size_batching.yaml

@@ -143,6 +143,7 @@ text:
     mode: text
     min_length: 0
     max_length: 255
+    pattern: "[A-Za-z0-9 ]+"
     initial_value: "Initial value"
     update_interval: 5.0s
 

tests/integration/test_api_message_size_batching.py

@@ -141,6 +141,9 @@ async def test_api_message_size_batching(
         assert text_input.max_length == 255, (
             f"Expected max_length 255, got {text_input.max_length}"
         )
+        assert text_input.pattern == "[A-Za-z0-9 ]+", (
+            f"Expected pattern '[A-Za-z0-9 ]+', got '{text_input.pattern}'"
+        )
 
         # Verify total entity count - messages of various sizes were batched successfully
         # We have: 3 selects + 3 text sensors + 1 text input + 1 number = 8 total