Function resolve_op_security 

pub fn resolve_op_security(
    op: &Operation,
    openapi: &OpenAPI,
    schemes: &[SchemeInfo],
) -> OpSecurity

Resolve the effective security requirements for an operation.

Semantics:

• operation.security == Some(vec![]) → explicit disable (no auth).
• operation.security == Some(non-empty) → use op-level requirements.
• operation.security == None → inherit openapi.security (doc-level default).

Each requirement object must reference exactly one supported scheme name to be accepted; requirements naming unknown schemes are dropped, and multi-key requirements (AND) are flagged via had_unsupported_and and otherwise dropped.