fix: preserve KnownHostsCommand arguments

[ilopezluna]

Summary

• parse KnownHostsCommand as a command with separately quoted arguments
• preserve its separators and quotes when computing effective configuration
• cover ESM and CommonJS parse/stringify behavior with the Remote-SSH regression case

Remote-SSH reparses and serializes the entire SSH config when adding a host. Previously this valid directive:

KnownHostsCommand "/opt/homebrew/bin/sbx" ssh known-hosts %H

was serialized as:

KnownHostsCommand "/opt/homebrew/bin/sbx ssh known-hosts %H"

This is the same directive-classification problem previously fixed for ProxyCommand in #48.

Related report: microsoft/vscode-remote-release#11780

Validation

• npm run build
• npm run lint
• focused ESM regression suite: 5 passing
• focused CommonJS regression suite: 5 passing
• all non-DNS-dependent ESM tests: 92 passing
• all non-DNS-dependent CommonJS tests: 82 passing

The complete local suite additionally runs canonical-domain tests that depend on resolving public DNS names; one could not resolve in this environment. GitHub CI will run the complete Node and Deno matrices.