Removing append to optimize memory usage

[donpui]

We run diagnostic with pprof (go tool pprof -alloc_space -cum http://localhost:8081/debug/pprof/heap) to check memory usage and made several changes to optimise, when sending large files via w-w CLI

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Code Review Checklist (to be filled out by reviewer)

• Description accurately reflects what changes are being made.
• Description explains why the changes are being made (or references an issue containing one).
• The PR appropriately sized.
• New code has enough tests.
• New code has enough documentation to answer "how do I use it?" and "what does it do?".
• Existing documentation is up-to-date, if impacted.

[piegamesde]

The CI consistently fails even after a couple of retrys, not really sure why.

[donpui]

Rollback append removal, otherwise we send two websocket packages...