chore(release): prepare dshell v0.6.2

[metah3m]

Summary

• cancel and reap SSH child processes when the transport closes
• run PAM session setup on the process leader for pam_loginuid compatibility
• prepare dshell 0.6.2 as a stable crate release

Release

• Planned tag: v0.6.2
• Dependency baseline: h3x 0.6.1
• Publish dshell 0.6.2 to crates.io

Verification

• Existing Ubuntu verification: cargo +nightly test --all-features (231 passed).
• GitHub Actions checks are the release gate.
• Local tests were not rerun per release instruction.

Release notes

Reliably tear down SSH child processes on transport close and keep PAM session setup on the process leader.