Updated the BaseTextAggregator to categorize aggregations

Modified the BaseTextAggregator type so that when text gets aggregated, metadata can
be associated with it. Currently, that just means a `type`, so that the aggregation
can be classified or described. Changes made to support this:
  - **IMPORTANT**: Aggregators are now expected to strip leading/trailing white space
    characters before returning their aggregation from `aggregation()` or `.text`. This
    way all aggregators have a consistent contract allowing downstream use to know how
    to stitch aggregations back together
  - Introduced a new `Aggregation` dataclass to represent both the aggregated `text` and
    a string identifying the `type` of aggregation (ex. "sentence", "word", "my custom
    aggregation")
  - **BREAKING**: `BaseTextAggregator.text` now returns an `Aggregation` (instead of `str`).
    To update: `aggregated_text = myAggregator.text` -> `aggregated_text = myAggregator.text.text`
  - **BREAKING**: `BaseTextAggregator.aggregate()` now returns `Optional[Aggregation]`
    (instead of `Optional[str]`). To update:
      ```
      aggregation = myAggregator.aggregate(text)
      if (aggregation):
        print(f"successfully aggregated text: {aggregation.text}") // instead of {aggregation}
      ```
  - `SimpleTextAggregator`, `SkipTagsAggregator`, `PatternPairAggregator` updated to
     produce/consume `Aggregation` objects.
  - All uses of the above Aggregators have been updated accordingly.

src/pipecat/tests/utils.py

@@ -203,8 +203,16 @@ async def run_test(
             if not isinstance(frame, EndFrame) or not send_end_frame:
                 received_down_frames.append(frame)
 
-        print("received DOWN frames =", received_down_frames)
-        print("expected DOWN frames =", expected_down_frames)
+        down_frames_printed = "["
+        for frame in received_down_frames:
+            down_frames_printed += f"{frame.__class__.__name__}, "
+        down_frames_printed += "]"
+        expected_frames_printed = "["
+        for frame in expected_down_frames:
+            expected_frames_printed += f"{frame.__name__}, "
+        expected_frames_printed += "]"
+        print("received DOWN frames =", down_frames_printed)
+        print("expected DOWN frames =", expected_frames_printed)
 
         assert len(received_down_frames) == len(expected_down_frames)