* caddytls: synchronize storage cleaner with TLS.Stop via context and WaitGroup
* Unify the storage cleanup synchronization to both tls and ech.
* Cannot embed the sync.WaitGroup directly as the TLS struct is copied.
* caddytls: propagate cancellable context to ECH rotation and add sync tests
Pass cancellable context to ECH key rotation so in-flight storage locks
and operations unblock when TLS.Stop is invoked. Add comprehensive tests
verifying TLS.Stop cleanly unblocks and waits for storage cleaner and
ECH workers.
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Co-authored-by: Zen Dodd <mail@steadytao.com>
