refactor: replace nested conditionals in get_var_attrs with declarative token registry

[bhagathkrishnacdac]

Summary
This PR refactors commands.py for improved code quality. This PR focuses on refactoring the CLI auto-completion logic to eliminate a massive if/elif chain in get_var_attrs.

Key Changes

• Declarative Token Map (TOKEN_REGISTRY): Established a centralized map of autocomplete tokens to their respective types, descriptors, and candidate-provider lists.
• Unified RPC Wrapper (_fetch_candidates): Introduced a standardized helper to wrap BESS RPC data queries, ensuring safe execution and uniform error-handling during active tab completion.
• Dynamic Fetchers: Extracted dynamic data-gathering logic (e.g., worker status, port lists, module classes, active traffic classes) into isolated, single-responsibility helper functions.
• Streamlined Dispatcher (get_var_attrs): Simplified the entry point to a lightweight lookup that uses inspect.signature to dynamically resolve parameter requirements for different candidate providers.

[Copilot]

Pull request overview

Refactors BESS CLI auto-completion token handling in bessctl by replacing a large conditional chain in get_var_attrs() with a declarative token registry and helper candidate fetchers, aiming to simplify maintenance of completion behavior.

Changes:

• Introduced helper fetchers (_fetch_candidates, _get_workers, _get_ports, etc.) to centralize RPC-backed candidate collection.
• Added a TOKEN_REGISTRY mapping tokens to (type, description, provider) to eliminate the large if/elif chain.
• Simplified get_var_attrs() into a registry lookup + provider dispatch.

Suppressed comments (2)

bessctl/commands.py:285

• [PORT_NUMBER] describes a port number but the text says "HTTP server address". This is user-facing help text shown during CLI guidance, so it should refer to the port.

    '[PORT_NUMBER]': ('int', 'HTTP server address to listen on (default: 5000)', []),

bessctl/commands.py:283

• [PAUSE_WORKERS] description dropped the default value information that existed previously, which is useful in the interactive help output. Consider restoring the default note.

    '[PAUSE_WORKERS]': ('pause_workers', 'determines whether to pause workers', 
                        ['pause', 'no_pause']),

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[andybavier]

get_var_attrs() currently uses the provider’s parameter count to decide whether to pass partial_word. That appears to break _get_modules(cli, include_star=False): it has two parameters, so MODULE and MODULE... are invoked as _get_modules(cli, partial_word). Any nonempty partial word is truthy and therefore enables include_star, adding * to completions which seems unintended.

Suggest wrapping all module lookups:

'MODULE': (..., lambda cli, word: _get_modules(cli)),
'MODULE...': (..., lambda cli, word: _get_modules(cli)),
'[MODULE]': (..., lambda cli, word: _get_modules(cli, True)),

[andybavier]

get_var_attrs() currently uses the provider’s parameter count to decide whether to pass partial_word. That appears to break _get_modules(cli, include_star=False): it has two parameters, so MODULE and MODULE... are invoked as _get_modules(cli, partial_word). Any nonempty partial word is truthy and therefore enables include_star, adding * to completions which seems unintended.

Suggest wrapping all module lookups:

'MODULE': (..., lambda cli, word: _get_modules(cli)),
'MODULE...': (..., lambda cli, word: _get_modules(cli)),
'[MODULE]': (..., lambda cli, word: _get_modules(cli, True)),