fix: harden idle timeout parsing

[hiSandog]

Summary

• avoid byte-splitting the idle timeout suffix so non-ASCII units return an error instead of panicking
• use checked multiplication when converting s/m/h values to milliseconds
• add parser regression coverage for Unicode units and overflow

Validation

• git diff --check
• cargo test parse_idle_timeout --manifest-path cli/Cargo.toml (not run: cargo is not installed in this local environment)

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