perf: Avoid generating str repr of table during rendering (#1015)

What's happening here is that
[`_repr_mimebundle_`](https://github.com/manzt/anywidget/blob/a49a872a9e2cd491e7597bc1e550d14352efc7b6/anywidget/widget.py#L76-L82)
creates **both** the rich HTML content **and** a plain text repr to show
in environments that don't support HTML rendering.

So it was taking 11.6 seconds to print the string repr of the Arrow
table, just to generate the `_repr_mimebundle_`.

I'm not clear if this is a regression or just an unhandled bug on the
arro3 side (kylebarron/arro3#432). I think
arro3 handles _long_ tables by taking the first and last `n` rows to
print. But it clearly doesn't handle very _wide_ rows at all.

### Change list

- This overrides
[`_repr_keys`](https://github.com/jupyter-widgets/ipywidgets/blob/df7836eb4509283a0bf14d7b4ac92bc30c11fc76/python/ipywidgets/ipywidgets/widgets/widget.py#L827-L843)
to ensure that the str repr of the `table` attribute is never generated.
I think this is the only key that should be very slow.

### Benchmark

99.9% faster rendering 😅 

On this branch:

```py
from lonboard import viz
from geodatasets import get_path
import geopandas as gpd
from IPython.display import display

gdf = gpd.read_file(get_path("nybb"))

%%time
m = viz(gdf)
# CPU times: user 112 ms, sys: 28.3 ms, total: 141 ms
# Wall time: 148 ms

%%time
display(m)
# CPU times: user 5.01 ms, sys: 1.41 ms, total: 6.43 ms
# Wall time: 5.64 ms
```

On main:

```py
from lonboard import viz
from geodatasets import get_path
import geopandas as gpd
from IPython.display import display

gdf = gpd.read_file(get_path("nybb"))

%%time
m = viz(gdf)
# CPU times: user 112 ms, sys: 28.3 ms, total: 141 ms
# Wall time: 148 ms

%%time
display(m)
# CPU times: user 11.6 s, sys: 262 ms, total: 11.9 s
# Wall time: 12 s
```

Closes #1014

Author: kylebarron

lonboard/layer/_base.py

@@ -31,7 +31,7 @@
 
 if TYPE_CHECKING:
     import sys
-    from collections.abc import Sequence
+    from collections.abc import Generator, Sequence
 
     import duckdb
     import geopandas as gpd
@@ -313,6 +313,17 @@ class BaseArrowLayer(BaseLayer):
 
     table: ArrowTableTrait
 
+    def _repr_keys(self) -> Generator[str, Any, None]:
+        # Avoid rendering `table` in the string repr
+        #
+        # By default, `_repr_mimebundle_` creates the rich HTML content **and** a plain
+        # text repr to show in environments that don't support rendering HTML. We want
+        # to avoid generating a str repr of any large values.
+        # https://github.com/developmentseed/lonboard/issues/1014
+        for key in super()._repr_keys():
+            if key != "table":
+                yield key
+
     def __init__(
         self,
         table: ArrowStreamExportable,