[thiyaguk09]

Description

Expose the highWaterMark option for File upload and download streams.

Impact

Users can tune stream buffer sizes to optimize throughput performance.

Changes

• Add optional highWaterMark?: number with TSDoc/JSDoc documentation to CreateReadStreamOptions and CreateWriteStreamOptions in src/file.ts, as well as MakeWritableStreamOptions in src/nodejs-common/util.ts.
• Extract highWaterMark in File#createReadStream and pass it to the underlying PassThroughShim stream returned to callers.
• Extract highWaterMark in File#createWriteStream and propagate it to the outer Writable, PassThroughShim, and duplexify streams, as well as to both resumable (resumableUpload.upload) and simple (File#startSimpleUpload_ / util.makeWritableStream) upload streams.

Testing

• Add unit test in test/file.ts verifying File#createReadStream sets readableHighWaterMark when highWaterMark is provided.
• Add unit tests in test/file.ts verifying File#createWriteStream sets writableHighWaterMark and propagates highWaterMark to both resumable and simple upload streams.
• Add unit tests in test/file.ts and test/nodejs-common/util.ts verifying highWaterMark propagation in startResumableUpload_, startSimpleUpload_, and util.makeWritableStream.

[gemini-code-assist]

Code Review

This pull request introduces support for configuring the stream highWaterMark (in bytes) for both readable and writable streams. It adds the highWaterMark option to CreateWriteStreamOptions, CreateReadStreamOptions, and MakeWritableStreamOptions, ensuring it is correctly propagated to underlying streams, including PassThroughShim, Writable, duplexify, and ProgressStream, as well as resumable and simple uploads. Comprehensive unit tests have been added to verify this propagation. There are no review comments, and I have no feedback to provide.