fix: give better error message when object not serializable

[tobymao]

No description provided.

[georgesittas]

LGTM, let's fix the title before merging because it's no longer true.

[georgesittas]

This applies for models, signals too, besides macros, so the message could be misleading. I'd do this instead:

Suggested change

	raise SQLMeshError(
	f"'{v}' cannot be serialized because it is a constant object. Import the module and call it from within the macro instead:\nimport module\n\ndef my_macro():\n module.{v}"
	)
	raise SQLMeshError(
	f"Object '{v}' cannot be serialized. If it's defined in a library, import the corresponding "
	"module and reference the object using its fully-qualified name. For example, the datetime "
	"module's 'UTC' object should be accessed as 'datetime.UTC'."
	)

This would print something like:

Object 'UTC' cannot be serialized. If it's defined in a library, import the corresponding module and reference the object using its fully-qualified name. For example, the datetime module's 'UTC' object should be accessed as 'datetime.UTC'.

[georgesittas]

We can also add Ellipsis here for completeness. According to literal_eval's docs:

Evaluate an expression node or a string containing only a Python literal or container display. The string or node provided may only consist of the following Python literal structures: strings, bytes, numbers, tuples, lists, dicts, sets, booleans, None and Ellipsis.