Extend the 'part' command unit tests to include partition lookup via
UUID.

This ensures that the 'number', 'start', and 'size' subcommands
consistently handle UUIDs as partition identifiers, maintaining
parity with the name-based lookup functionality.

Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

Add unit tests for the 'part' command, specifically for the 'number',
'start', and 'size' subcommands.

These tests establish a baseline for the current partition lookup
functionality by name. This foundation will be used by subsequent
patches to extend the command, ensuring consistent behavior as new
features are introduced.

Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Reviewed-by: Simon Glass <sjg@chromium.org>