fix(storage): optimize stream download throughput and eliminate write latency

[thiyaguk09]

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Fixes #<issue_number_goes_here> 🦕

[gemini-code-assist]

Code Review

This pull request updates the PassThroughShim class in handwritten/storage/src/util.ts by changing the order of state updates and event emissions, calling super._write synchronously, implementing _writev for vectorized writes, and updating _final to delegate to the base class when available. The feedback points out a TypeScript compilation issue in the new _writev method where the chunks parameter is typed with chunk: never, which causes errors under strict compilation, and suggests changing it to any.