Quote bitcoin kubectl command arguments

[Asylian21]

Summary

• build bitcoin RPC and log kubectl commands with shlex.join so dynamic arguments are shell-quoted consistently
• avoid shell=True when reading captured message files
• add a regression check that shell metacharacters remain single command arguments

Validation

• PYTHONPATH=.:src:resources/scenarios:test uv run --frozen python test/bitcoin_rpc_args_test.py
• uvx ruff check src/warnet/bitcoin.py test/bitcoin_rpc_args_test.py
• git diff --check