Add optional colorized output support

Description

This issue adds optional colorized terminal output to ros2cli. Colorization is off by default and can be enabled in two ways:

• Set the environment variable ROS_COLORIZED_OUTPUT=1 (requires stdout to be a TTY)
• Pass the --color flag on the command line (e.g. ros2 --color topic echo /chatter)

Motivation

ros2cli output — especially from commands like ros2 topic echo, ros2 interface show, and ros2 param dump — is often dense, structured text (YAML, IDL, key-value pairs). Without color, it is difficult to quickly distinguish field names from values, ROS type strings from plain text, or section headers from content. Colorized output is a standard ergonomic feature in modern CLI tools and has been a recurring community request.

Design / Implementation Considerations

Modified: ros2cli/cli.py

• Adds --color CLI argument
• Activates ColoringStdout wrapping when color is enabled, selecting the appropriate colorizer for the active command/verb

New file: ros2cli/color.py

• Introduces a Colorizer base class and an extensible registry keyed by (command, verb) pairs
• DefaultColorizer applies generic ANSI heuristics (ROS paths, type strings, YAML keys) as a fallback for unregistered commands
• ColoringStdout wraps sys.stdout and colorizes output line-by-line
• Built-in colorizers registered for: ros2 (help), topic echo, topic hz, topic bw, topic info, param get, param dump, interface show, component list
• Third-party packages can register custom colorizers via ros2cli.color.register(command, verb, colorizer)

Additional Information

No response

Start by reading ros2cli/cli.py to trace argument handling and stdout setup, then review the proposed ros2cli/color.py interfaces and registered command/verb pairs. Verify that both ROS_COLORIZED_OUTPUT=1 and --color enable TTY-aware colorization, while default output remains unchanged across the listed commands.