fix: convert all content values to strings

[mmikita95]

Adds a _prepare_value for StreamsyncUIManager class, to utilize inside _create_component. For dict, it uses json.dumps, and casts to str for the rest of the types. Allows to use Python types when defining content for CMCs, for example:

ui.SliderInput({"minValue": 0, "maxValue": 300, "stepSize": 1}) # uses int literals

By default, this triggers TypeError: template.replace is not a function on the frontend; this fix allows to avoid it.