Function load_spec_document 

pub fn load_spec_document(path: &str) -> SpecResult<SpecDocument>

Load a spec document from disk.

Parsing is format-directed:

• .json files are parsed as JSON documents only.
• .itsd files (or payloads with the itsd magic envelope) are decoded as binary documents.
• Otherwise, JSON parsing is attempted and JSON errors are reported directly without a binary fallthrough.