fix: size flags accept the Kubernetes Gi spelling

[CMGS]

Why

--memory, --storage, --data-disk size= and gc --snapshot-size each handed their value straight to go-units, which reads 20G and 20GiB but rejects 20Gi, so a Kubernetes-shaped quantity failed on cocoon while cocoon-macos carried its own normaliser in front of the parser exported by #242.

What

types.ParseSize is the one rule for the family: trim, append B to a trailing i, then go-units. The four flags call it; ParseDataDiskSpec too. Every unit stays binary (20G is 20 GiB, as before); the CLI page says so next to the size flags. cocoon-macos can delete its parseSize at its next pin bump.

Evidence

• GOWORK=off go build ./... on darwin and linux, go test ./types/ ./cmd/core/ ./cmd/others/ ok, make lint 0 issues on both platforms, asl clean, no comment beyond the one godoc.
• Table test: 20G, 20Gi, 20GiB, 20gi all 20 GiB; 512Mi trimmed; bare 1024; 20i, empty and abc refused.

Closes #245