fix: validate lakehouse upload files before streaming the payload

[francoischalifour]

Summary

• Check upload paths with statSync before building the lakehouse request so missing files and directories fail fast.
• Pass the file size through the upload request instead of re-reading the file to size the progress reporter.
• Add tests for the non-buffering upload path and for rejecting missing files and directories.

Testing

• Added unit tests covering upload request construction and command-level file validation.

Risks

• Behavior now depends on filesystem metadata instead of attempting to open the file contents, which should preserve the same user-facing error while avoiding unnecessary buffering.

[redox]

Love it