feat: cwriter for wasm v7

[Icemap]

No description provided.

[wanshicheng]

Your commits does not support GOOS=wasip1 and GOARCH=wasm

[Solaris-star]

This is a superset of #132 — it adds the same WASM stubs plus util_wasm.go for the ioctl constant. Two issues:

1. Build tags: uses the old //+build syntax. Go 1.17+ prefers //go:build. #132 already has the correct syntax — worth aligning.

2. IsTerminal returns true: same concern as #132 — WASM has no terminal, so false is more accurate. Callers checking IsTerminal to decide between TTY and plain output would get the wrong branch.

Recommend consolidating #132 and #133 into a single PR with //go:build tags and IsTerminal → false. The core approach (dummy Writer, no-op GetSize) is correct.