feat(bigframes): Support Expression objects in create_model options

This change allows the `options` parameter of `bigframes.bigquery._operations.ml.create_model` to accept BigFrames `Expression` objects. These expressions are compiled to SQL scalar expressions and included in the generated `CREATE MODEL` DDL statement.

- Added `bigframes.core.expression.Expression` type support in the `options` dict.
- Updated `create_model_ddl` to handle compiling expressions using `expression_compiler`.
- Added `test_create_model_expression_option` snapshot test to verify the generated "golden SQL", using an expression that calls a function on a literal value (e.g. 0.1 * 10).

Co-authored-by: tswast <247555+tswast@users.noreply.github.com>

Author: google-labs-jules[bot]

packages/bigframes/tests/unit/core/sql/test_ml.py

@@ -106,7 +106,9 @@ def test_create_model_expression_option(snapshot):
     # e.g. 0.1 * 10
     literal_expr = ex.ScalarConstantExpression(0.1, dtypes.FLOAT_DTYPE)
     multiplier_expr = ex.ScalarConstantExpression(10, dtypes.INT_DTYPE)
-    math_expr = ex.OpExpression(op=numeric_ops.mul_op, inputs=(literal_expr, multiplier_expr))
+    math_expr = ex.OpExpression(
+        op=numeric_ops.mul_op, inputs=(literal_expr, multiplier_expr)
+    )
 
     sql = bigframes.core.sql.ml.create_model_ddl(
         model_name="my_model",