scripts: west: commands: completion: zsh: update completion script with new west arguments

[henrikbrixandersen]

Is your enhancement proposal related to a problem? Please describe.
The Bash completion script for West has seen a few updates that are not present in the Zsh completion script. Please see the following PRs for details:

• scripts: west: commands: completion: add bash completion for twister #72167
• scripts: west: commands: build: add --shield argument for specifying shields #72720

Describe the solution you'd like
The Zsh shell completion script for West should be updated as well.

Describe alternatives you've considered
None.

Additional context
I do not use the Zsh shell and therefore have no way of verifying any changes to its completion files.