feat: implement StuckLoopHook for repeated dispatch termination

[ForeverAngry]

What

Adds StuckLoopHook to rig_compose::reliability to detect and terminate infinite tool-dispatch loops when the model requests the exact same tool invocation repeatedly.

Why

This satisfies the final piece of the Govern tool/result reliability roadmap item: terminating repeated-loops around dispatch to prevent runway costs in cases where models are repeatedly failing to adapt to a tool outcome and re-issuing identical requests.

[Copilot]

Pull request overview

Adds a StuckLoopHook to rig_compose::reliability that implements ToolDispatchHook and terminates dispatch when the same tool invocation (identified via ToolCallFingerprint) is requested more than max_identical_calls times. Re-exports the new type from the crate root, updates the changelog, and adjusts the roadmap to reflect that stuck-loop, retry, and result-size policies are now covered.

Changes:

• New StuckLoopHook with before_invocation returning Terminate { reason } once the per-fingerprint count exceeds the threshold, plus two async unit tests covering threshold and multi-tool tracking.
• Public re-export of StuckLoopHook from src/lib.rs.
• Documentation updates in CHANGELOG.md and ROADMAP.md.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/reliability.rs	Adds StuckLoopHook struct, ToolDispatchHook impl, module-level doc bullet, and tests.
src/lib.rs	Re-exports StuckLoopHook from the reliability module.
ROADMAP.md	Drops retry/result-size/stuck-loop from the list of unbuilt policies.
CHANGELOG.md	Adds an "Added" entry under Unreleased noting the new hook.

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