feat: Implement GeoSeries scalar operators

This commit implements 6 new GeoSeries scalar properties and methods:
- `is_empty`
- `geom_type`
- `is_ring`
- `is_simple`
- `is_valid`
- `union`

This change includes:
- Defining the new operations in `bigframes/operations/geo_ops.py`.
- Implementing the compilation logic for the Ibis backend.
- Adding the new properties and methods to the `GeoSeries` class.
- Adding system tests for all new features.

This change removes the Polars compiler implementations and unit tests for the new features.

Author: google-labs-jules[bot]

bigframes/core/compile/polars/compiler.py

@@ -437,8 +437,6 @@ def _(self, op: ops.ArrayReduceOp, input: pl.Expr) -> pl.Expr:
                     f"Haven't implemented array aggregation: {op.aggregation}"
                 )
 
-
-
     @dataclasses.dataclass(frozen=True)
     class PolarsAggregateCompiler:
         scalar_compiler = PolarsExpressionCompiler()