fix: coerce filter expressions before simplifying (#6935)

## Summary

Fix `Planner::optimize_expr` so expression type coercion runs before
simplification. This matches DataFusion's normal plan pipeline where
analyzer type coercion runs before optimizer simplification.

This matters for immutable UDFs with literal arguments. With the
previous order, simplification could evaluate a constant UDF call before
`Int64` literals were coerced to the UDF's expected `Float64` inputs.
For geospatial filters, `st_point(0, 0)` could reach the geo UDF as
integer arrays and panic during the UDF's strict float downcast.
`st_point(0.0, 0.0)` worked because the literals were already `Float64`.

## Repro Demo

This is a standalone Python repro script. It is not added to the repo.

```python
import tempfile

import lance
import numpy as np
import pyarrow as pa
from geoarrow.rust.core import point, points


def run_filter(ds, expr):
    table = ds.to_table(filter=expr)
    values = table.to_pydict()
    print(f"{expr} -> {table.num_rows} rows: {values}")
    assert table.num_rows == 1


with tempfile.TemporaryDirectory() as tmpdir:
    point_array = points([np.array([1.0, 10.0]), np.array([2.0, 10.0])])
    schema = pa.schema([pa.field(point("xy")).with_name("point")])
    table = pa.Table.from_arrays([point_array], schema=schema)
    ds = lance.write_dataset(table, f"{tmpdir}/geo_filter.lance")

    run_filter(ds, "st_distance(point, st_point(0.0, 0.0)) < 5")
    run_filter(ds, "st_distance(point, st_point(0, 0)) < 5")
```

Observed before the fix:

```text
st_distance(point, st_point(0.0, 0.0)) < 5 -> 1 rows: {'point': [{'x': 1.0, 'y': 2.0}]}
thread 'lance_background_thread' panicked at .../arrow-array-58.3.0/src/cast.rs:849:33:
primitive array
RuntimeError: Task was aborted
```

Observed after the fix:

```text
st_distance(point, st_point(0.0, 0.0)) < 5 -> 1 rows: {'point': [{'x': 1.0, 'y': 2.0}]}
st_distance(point, st_point(0, 0)) < 5 -> 1 rows: {'point': [{'x': 1.0, 'y': 2.0}]}
```