test: add CLI unit tests, integration tests, and criterion benchmarks

[ankarhem]

Summary

• M3: 20 unit tests for cli.rs covering argument parsing, validation, limit bounds, and sort-direction enums
• M4: 4 integration tests in tests/cli_integration.rs (--help, --version, no-args, unknown-command)
• M13: Criterion benchmarks in benches/ for timerange parsing and JSON serialization/deserialization

Test plan

• cargo check passes
• All 229 tests pass (205 existing + 20 new unit + 4 integration)
• cargo check --benches compiles cleanly