Pure-Go bindings via wasm32-wasip1 + wazero (CGO_ENABLED=0)

I've published Go bindings that take a different approach from #30, and
wanted to check whether you'd want them linked from the README, upstreamed,
or simply left downstream.

https://github.com/xusenlin/go-anydoc

#30 binds the crate through cgo with prebuilt per-platform archives. This one
compiles the crate to a `wasm32-wasip1` command module, embeds it with
`go:embed`, and runs it under wazero. The trade-offs are genuinely different,
so I don't think it displaces #30:

- `CGO_ENABLED=0`, cross-compiles wherever Go does — verified on
linux/{amd64,arm64,riscv64,ppc64le,386,s390x}, darwin, windows, freebsd
- one 4.83 MB wasm artifact instead of a per-platform archive matrix
- self-contained single binary, no external process, no system deps
- the cost: interpreted execution. A 1 KB docx converts in 5 ms, but one with
a 5 MB uncompressed body takes 16.9 s against 1.1 s compiled. There's an
opt-in `WithCompiler()` for callers who can afford ~2 s and 576 MB at
startup.

One thing worth noting given #67: because the crate runs as a sandboxed wasm
guest, the lopdf `SIGABRT` path surfaces as a returned error rather than
killing the host process — wazero bounds guest call depth and a wasm guest
can't signal the host. A cgo binding has no such containment.

The exit-code table between my WASI shim and the Go error types is pinned to
`ConvertError::code()`, so I'd like to know how stable you consider that and
`to_markdown_bytes` to be across releases. The crate is pinned with `=` and
rebuilds go through a reviewed PR, but I'd rather track your intent than guess.

Happy to move any of this into the repo if a `go/` directory using the wasm
path is something you'd want.

Start by reviewing the linked go-anydoc implementation and the repository README, then examine the WASI shim’s mapping to ConvertError::code() and to_markdown_bytes. The scope is not yet defined: confirm whether the desired outcome is a README link, an upstream go/ directory, or no repository change.

Written by the indexing model from the issue text.