fix: resolve remote 'cd' path handling and escaping in ssh caused by work on #8

Introduced 'build_cd_command' in 'lua/sshfs/lib/ssh.lua' to correctly
handle tilde expansion and safely escape paths for remote 'cd'
operations. This resolves a regression where remote 'cd' functionality
was broken due to improper path handling.

Updates 'Ssh.build_command' to utilize the new helper for robust and
secure remote directory navigation.

Ref #8