fix(cli): download-output command handles UNC paths

[gahyusuh]

What was the problem/requirement? (What/Why)

The download-output CLI command failed to download job outputs with UNC root paths, resulting in error that looks like below.

Download failed: Path \10.7.1.50\TestOutputShare\work is not an absolute path.

The current logic for checking if a path format is Posix or Windows cannot handle UNC path format. It is just doing a naive string check on the root paths.

What was the solution? (How)

• Updated to properly handle UNC paths. Instead of the existing naive string check, it is now relying on the rootPathFormat property in job's manifests (the value is either "windows" or "posix") to determine the submitting OS of the job.
• Fixed or added unit tests to align with the changes, ensuring all tests pass.

What is the impact of this change?

The download-output command can now support jobs with UNC root paths.

How was this change tested?

• All unit tests, including modified and newly added ones, passed successfully.
• Done some manual end-to-end tests including cross-platform scenarios, confirming that it worked as expected.
  • Downloading Linux-submitted job outputs on Windows: prompted users for an alternative root path to download to.
  • Downloading outputs from job with UNC format root paths on Windows: no errors, downloading files to the right location.
  • Downloading Windows-submitted job outputs on Linux: prompted users for an alternative root path to download to.
  • Downloading outputs from jobs with UNC format root paths on Linux: prompted users for an alternative root path to download to.

Was this change documented?

No.

Is this a breaking change?

No.

[epmog]

LGTM. Ship it