Warn instead of raise on `start_dt`-trimmed frames

Downgrade the `start_dt`-trimming check in `open_history_client()`
from a `RuntimeError` raise to a warning log, allowing the caller
to still receive a (shorter) frame of bars (though we may need to still
specially handle such cases in the backfiller's biz logic layer).

Deats,
- add `trimmed_bars.size` guard to skip check on empty results.
- change condition to `>=` and log a warning with the short-frame
  size instead of raising.
- comment-out `raise RuntimeError` and breakpoint for future
  removal once confident.
- add docstring-style comment on `start_dt=` kwarg noting that
  `Client.bars()` doesn't truly support it (uses duration-style
  queries internally).

(this commit msg was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code

piker/brokers/ib/feed.py

@@ -201,6 +201,15 @@ async def open_history_client(
                 fqme,
                 timeframe,
                 end_dt=end_dt,
+
+                # XXX WARNING, we don't actually use this inside
+                # `Client.bars()` since it isn't really supported,
+                # the API instead supports a "duration" of time style
+                # from the `end_dt` (or at least that was the best
+                # way to get it working sanely)..
+                # 
+                # SO, with that in mind be aware that any downstream
+                # logic based on this may be mostly futile Xp
                 start_dt=start_dt,
             )
             latency = time.time() - query_start
@@ -278,19 +287,27 @@ async def open_history_client(
                 trimmed_bars = bars_array[
                     bars_array['time'] >= start_dt.timestamp()
                 ]
-                if (
-                    trimmed_first_dt := from_timestamp(trimmed_bars['time'][0])
-                    !=
-                    start_dt
-                ):
-                    # TODO! rm this once we're more confident it never hits!
-                    # breakpoint()
-                    raise RuntimeError(
-                        f'OHLC-bars array start is gt `start_dt` limit !!\n'
-                        f'start_dt: {start_dt}\n'
-                        f'first_dt: {first_dt}\n'
-                        f'trimmed_first_dt: {trimmed_first_dt}\n'
-                    )
+                # XXX, should NEVER get HERE!
+                if trimmed_bars.size:
+                    trimmed_first_dt: datetime = from_timestamp(trimmed_bars['time'][0])
+                    if (
+                        trimmed_first_dt
+                        >=
+                        start_dt
+                    ):
+                        msg: str = (
+                            f'OHLC-bars array start is gt `start_dt` limit !!\n'
+                            f'start_dt: {start_dt}\n'
+                            f'first_dt: {first_dt}\n'
+                            f'trimmed_first_dt: {trimmed_first_dt}\n'
+                            f'\n'
+                            f'Delivering shorted frame of {trimmed_bars.size!r}\n'
+                        )
+                        log.warning(msg)
+                        # TODO! rm this once we're more confident it
+                        # never breaks anything (in the caller)!
+                        # breakpoint()
+                        # raise RuntimeError(msg)
 
                 # XXX, overwrite with start_dt-limited frame
                 bars_array = trimmed_bars