docs(udfs): improve udf docstring examples (#9079)

UDF arguments need to be Ibis expressions. In the existing docstring
examples
for the UDF decorators, it can be unclear that the integers being passed
to
`add_one` are implicitly converted to Ibis literals.

To make it clearer, I've added memtables to all the examples, and used
pandas-
and pyarrow-specific functions to the examples.

ibis/expr/operations/udf.py

@@ -296,13 +296,44 @@ def python(
         Examples
         --------
         >>> import ibis
+        >>> ibis.options.interactive = True
+        >>> t = ibis.memtable(dict(int_col=[1, 2, 3], str_col=["a", "b", "c"]))
+        >>> t
+        ┏━━━━━━━━━┳━━━━━━━━━┓
+        ┃ int_col ┃ str_col ┃
+        ┡━━━━━━━━━╇━━━━━━━━━┩
+        │ int64   │ string  │
+        ├─────────┼─────────┤
+        │       1 │ a       │
+        │       2 │ b       │
+        │       3 │ c       │
+        └─────────┴─────────┘
+        >>> @ibis.udf.scalar.python
+        ... def str_magic(x: str) -> str:
+        ...     return f"{x}_magic"
         >>> @ibis.udf.scalar.python
-        ... def add_one(x: int) -> int:
+        ... def add_one_py(x: int) -> int:
         ...     return x + 1
-        >>> expr = add_one(2)
-        >>> con = ibis.connect("duckdb://")
-        >>> con.execute(expr)
-        3
+        >>> str_magic(t.str_col)
+        ┏━━━━━━━━━━━━━━━━━━━━━━┓
+        ┃ str_magic_0(str_col) ┃
+        ┡━━━━━━━━━━━━━━━━━━━━━━┩
+        │ string               │
+        ├──────────────────────┤
+        │ a_magic              │
+        │ b_magic              │
+        │ c_magic              │
+        └──────────────────────┘
+        >>> add_one_py(t.int_col)
+        ┏━━━━━━━━━━━━━━━━━━━━━━━┓
+        ┃ add_one_py_0(int_col) ┃
+        ┡━━━━━━━━━━━━━━━━━━━━━━━┩
+        │ int64                 │
+        ├───────────────────────┤
+        │                     2 │
+        │                     3 │
+        │                     4 │
+        └───────────────────────┘
 
         See Also
         --------
@@ -366,13 +397,32 @@ def pandas(
         --------
         ```python
         >>> import ibis
+        >>> ibis.options.interactive = True
+        >>> t = ibis.memtable(dict(int_col=[1, 2, 3], str_col=["a", "b", "c"]))
+        >>> t
+        ┏━━━━━━━━━┳━━━━━━━━━┓
+        ┃ int_col ┃ str_col ┃
+        ┡━━━━━━━━━╇━━━━━━━━━┩
+        │ int64   │ string  │
+        ├─────────┼─────────┤
+        │       1 │ a       │
+        │       2 │ b       │
+        │       3 │ c       │
+        └─────────┴─────────┘
         >>> @ibis.udf.scalar.pandas
-        ... def add_one(x: int) -> int:
-        ...     return x + 1
-        >>> expr = add_one(2)
-        >>> con = ibis.connect(os.environ["SNOWFLAKE_URL"])  # doctest: +SKIP
-        >>> con.execute(expr)  # doctest: +SKIP
-        3
+        ... def str_cap(x: str) -> str:
+        ...     # note usage of pandas `str` method
+        ...     return x.str.capitalize()
+        >>> str_cap(t.str_col)  # doctest: +SKIP
+        ┏━━━━━━━━━━━━━━━━━━━━━━━┓
+        ┃ string_cap_0(str_col) ┃
+        ┡━━━━━━━━━━━━━━━━━━━━━━━┩
+        │ string                │
+        ├───────────────────────┤
+        │ A                     │
+        │ B                     │
+        │ C                     │
+        └───────────────────────┘
         ```
 
         See Also
@@ -437,13 +487,22 @@ def pyarrow(
         --------
         >>> import ibis
         >>> import pyarrow.compute as pc
+        >>> from datetime import date
+        >>> ibis.options.interactive = True
+        >>> t = ibis.memtable(
+        ...     dict(start_col=[date(2024, 4, 29)], end_col=[date(2025, 4, 29)]),
+        ... )
         >>> @ibis.udf.scalar.pyarrow
-        ... def add_one(x: int) -> int:
-        ...     return pc.add(x, 1)
-        >>> expr = add_one(2)
-        >>> con = ibis.connect("duckdb://")
-        >>> con.execute(expr)
-        3
+        ... def weeks_between(start: date, end: date) -> int:
+        ...     return pc.weeks_between(start, end)
+        >>> weeks_between(t.start_col, t.end_col)
+        ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
+        ┃ weeks_between_0(start_col, end_col) ┃
+        ┡━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┩
+        │ int64                               │
+        ├─────────────────────────────────────┤
+        │                                  52 │
+        └─────────────────────────────────────┘
 
         See Also
         --------