fix: ensure the module compiles on unsupported platforms

[murfffi]

skip but compile tests on unsupported platforms

[gemini-code-assist]

Code Review

This pull request introduces WebAssembly test support in the Makefile, updates build tags to use the unix constraint, and adds a fallback tryPeek implementation for unsupported platforms. The review feedback highlights two main issues: first, the export PATH command in the Makefile's test-wasm target runs in a separate subshell and will not affect the subsequent go test command; second, the platform check in TestDo unnecessarily skips tests on other supported Unix-like platforms like FreeBSD or AIX.

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