fix(cli): add defensive type guard to parseDimension to prevent runtime crashes

[SyedaQurratAI]

Fixes #106

[SyedaQurratAI]

The local tests pass (272 passed), but conformance.test.ts fails and times out due to a 404 network resolution error on @terrazzo/token-types@^2.4.0 from npm registry. This seems to be an upstream environment issue.

[davideast]

Thank you @SyedaQurratAI! I fixed the terrazo issue so this should hopefully pass.

[davideast]

Hey @SyedaQurratAI, thank you for jumping on this. I just realized that this is already fixed. Your earlier PR #79 added the type guard to parseDimensionParts, which is the right place for it since all callers benefit from the check there. That fix was on main but hadn't been published yet when #106 was filed. We just shipped it in v0.3.0 (PR #108), so the published build now includes your fix.

Going to close this one since the issue is resolved. Please let me know if I'm mistaken though! Thank you for both contributions!