Fix request handler and routing state isolation

[dkropachev]

Summary

• disable AWS middleware handler caching so mutable retry/query-plan state remains request-scoped
• distinguish handler instances from handler option objects and merge Node/Fetch options with Alternator connection settings
• recognize FetchHttpHandler instances across duplicate package installations to avoid decoding compressed responses twice
• keep foreground discovery deadline timers referenced so awaited refreshes always settle
• correct the README TLS example to use the documented HTTPS scheme and port

Review validation

Four reported runtime defects were reproduced before applying these fixes and now have regression coverage. The reported claim that TLS options should automatically select HTTPS was not treated as a runtime defect: the public API and documentation define scheme as the transport selector and tls as HTTPS-agent configuration. The contradictory options example was corrected instead.

Verification

• npm run typecheck
• npm run lint
• npm test (82 tests)
• npm run build