Fix: handle nullish values in template sinks with ?? operator

[the-matrixneo]

This PR addresses a bug where plain objects with a primitive .value property { value: 0 }) were incorrectly processed by the rml parser. these effects were considered

• rendering as HTML content <div>${expr}</div>.
• when rendered inside an element's attribute <input value="${expr}">.

The Fix:

• new logical check has been added to the beginning of the data sink processing logic in the main rml function.
• this check now correctly identifies these "value-wrapper" objects and extracts their primitive value.

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