Cardano Updates

refactor(cli): unify instance info keys for start/inspect

Standardize the keys used for instance information in both the
`testnet_start` and `get_testnet_info` functions. Replace "pid" and
"logfile" with "start_pid" and "start_logfile" for consistency. Also,
ensure the "dir" key is always present. This improves clarity and
reduces confusion when consuming instance metadata.

docs(readme): add installation instructions for nix and pip

Add installation instructions to the README.

docs(readme): improve getting started instructions

docs(readme): add testnet creation and management guide

Expand the README with basic instructions for creating, listing,
inspecting, and stopping Cardonnay testnet instances. Includes example
commands and expected outputs for each step.

feat: add bash completion script for cardonnay

Introduce a dedicated bash completion script for the cardonnay CLI in
the completions directory. Update the development shell setup in
flake.nix to source this script instead of evaluating the completion
inline.

feat(readme): add centered logo image to README

Added a centered logo image to the README using HTML for alignment and
custom width.

refactor(cli): clarify "testnet cluster" terminology

Update CLI help messages and log outputs to consistently use "testnet
cluster" instead of "testnet" for improved clarity. This affects command
descriptions, print statements, and error logs in both the main CLI and
control commands. No functional changes were made.

feat(cli): add stop-all command to stop all testnet instances

Introduce a new CLI command `stop-all` that stops all running testnet
instances in the specified working directory. This command iterates over
all running instances, kills their processes, and stops their testnets.
Also, improve help texts for related commands for clarity.

refactor(cli): check supervisor bin only for actions

Previously, all cluster control commands checked for the presence of all
required binaries, even when only supervisor-related actions were needed.
This change introduces a `has_supervisorctl` utility to check only for the
`supervisorctl` binary where appropriate, and limits full environment
sanity checks to where they are strictly necessary. This improves
granularity and reduces unnecessary checks.

refactor: centralize testnet state constants

Move testnet state strings ("started", "starting", "stopped") to a new
consts.States class for consistency and maintainability. Update all
references in cli_control.py, cli_create.py, and inspect_instance.py to
use the new constants.

feat(cluster): improve cluster start checks and UX

Replace PID file check with socket existence check to determine if the
cluster is already running, making the detection more robust. Add rocket
emoji to the "Cluster started" message for better user feedback. Also,
add shellcheck disables for variables used in sourced functions.

feat(cli): add colorized output and logging

Introduce colorized output for CLI messages and logging. Add a new
`colors` module with ANSI color codes, and a `color_logger` module for
colorized log formatting. CLI commands now print status messages in
green for better visibility. Color usage is configurable via environment
variables: respects `NO_COLOR`, `CLICOLOR`, and `CLICOLOR_FORCE`.

refactor(cli): replace LOGGER.info with print for user messages