[+] add diff command, json logging, pinned annotation, --log-level support
1. add cli/diff.py with parse_compiled, compute_diff, format_diff;
2. diff shows added/removed packages, version changes;
3. add --diff-url and --diff-checksum BooleanOptionalAction flags (off by default);
4. move # pinned annotation to trailing comment on package spec line;
5. update download and diff parsers to strip trailing # comments;
6. add test_diff.py with parse, compute, format and end-to-end tests;
7. add json_formatter_t and format_t enum to commands_typed/logging.py;
8. add log_dir, log_name, max_bytes, backup_count, use_console params to setup();
9. add --log-level DEBUG|INFO|WARNING|ERROR to archlinux cli/main.py;
10. wire pr34_logging.setup with json formatter in main.py;
LLM
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