Add PhysicalExpr::is_volatile

We already have this for logical expressions:

https://github.com/apache/datafusion/blob/ad100fbd663eee85d1e1105cff338a21f33b9855/datafusion/expr/src/expr.rs#L2011-L2030


We dealt with the special case of functions in https://github.com/apache/datafusion/issues/16545 but I think it would be good to implement methods for the trait itself which seems clearer and more robust

	/// Returns true if the expression node is volatile, i.e. whether it can return
	/// different results when evaluated multiple times with the same input.
	/// Note: unlike [`Self::is_volatile`], this function does not consider inputs:
	/// - `rand()` returns `true`,
	/// - `a + rand()` returns `false`
	pub fn is_volatile_node(&self) -> bool {
	matches!(self, Expr::ScalarFunction(func) if func.func.signature().volatility == Volatility::Volatile)
	}

	/// Returns true if the expression is volatile, i.e. whether it can return different
	/// results when evaluated multiple times with the same input.
	///
	/// For example the function call `RANDOM()` is volatile as each call will
	/// return a different value.
	///
	/// See [`Volatility`] for more information.
	pub fn is_volatile(&self) -> bool {
	self.exists(\|expr\| Ok(expr.is_volatile_node()))
	.expect("exists closure is infallible")
	}

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Add PhysicalExpr::is_volatile #17318

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Add PhysicalExpr::is_volatile #17318

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