Add escape for scalars to binding during union handling

[wild-endeavor]

Tracking issue

Related to flyteorg/flyte#5321. This was discovered while implementing that PR.

Why are the changes needed?

The main issue is highlighted in the test added to the test type engine file. When you call TypeEngine.to_literal on a Union type, you should get back a Flyte literal with a Union message. This was happening correctly in the Type Engine but for some reason this wasn't happening for Binding Data.

That is, if you had

@task
def say_hello(a: int | str) -> str:
    print(f"Type is {type(a)}")
    if type(a) == str:
        return f"Hello, {a}!"
    return "Hello, World!"

@workflow
def hello_world_wf()-> str:
    res = say_hello(a="world")
    return res

the node for the say_hello invocation was being bound to a BindingData Literal Scalar that was just the raw string "world", not a Union that contained that string literal.

What changes were proposed in this pull request?

This adds an escape mechanism and some comments in the binding data from python std function.

How was this patch tested?

Before: https://www.test.cluster/console/projects/flytesnacks/domains/development/executions/f6ba77e8684e94e1092a
After: https://www.test.cluster/console/projects/flytesnacks/domains/development/executions/f06eaea2298ad4884952
Both runs succeed.

Before: https://www.test.cluster/api/v1/workflows/flytesnacks/development/unions.hello_world_wf/4jItAJN7eckVByTXKxjsPg
After: https://www.test.cluster/api/v1/workflows/flytesnacks/development/unions.hello_world_wf/gmbOol0QMeiiHF_y99A97g
Note the after definition binds the node to a union literal, not a plain scalar.

Setup process

Screenshots

Check all the applicable boxes

• I updated the documentation accordingly.
• All new and existing tests passed.
• All commits are signed-off.

Related PRs

Docs link

[wild-endeavor]

cc @MortalHappiness can you take a look at this? i think with this we can revert some of the changes in your pr...

[MortalHappiness]

LGTM