Function create_signature_context 

pub fn create_signature_context() -> SignatureContext

Create a SignatureContext with LibQSignatureProvider already installed (ML-DSA and SLH-DSA from lib-q-sig defaults; FN-DSA when the fn-dsa feature is enabled on this crate).

This is the umbrella-crate entry point: lib_q_core::create_signature_context returns an empty context for composition in leaf crates; libq::create_signature_context wires the production signature backend used by this workspace.