Add must-use authorization decisions and bound authorize helper

[hardbyte]

Awaited authorization decisions could be silently discarded. Add useful #[must_use] diagnostics to AccessEvaluation, GrantResult, and VetoResult, plus bound.authorize(&invoice).await? for enforcement at application boundaries. Method-level attributes on evaluate and evaluate_by also warn when their awaited batch results are discarded.

authorize returns Result<(), AccessError> by delegating directly to check(...).await.into_result(). It preserves denial versus indeterminate classification and complete error evidence without adding an evaluator. Documentation explains that must_use catches accidental omissions but still permits deliberate bypass.

Validation: formatting, Clippy with warnings denied, workspace build, all-target/all-feature tests, and doctests. Contract tests cover grants, denials, indeterminate outcomes, veto short-circuiting, preserved evidence, and one evaluation per applicable policy. Compile-fail doctests verify discarded awaited decisions fail under deny(unused_must_use) for all three result types and both batch methods.

Closes #68.

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-19T04:44:53.155772Z	11e9e56	PR opened

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