Add a new "mila run" command

[lebrice]

mila_run_demo.mp4

[Copilot]

Pull Request Overview

This PR adds a new mila run command that executes commands across multiple remote clusters in parallel. The command can either run on all clusters with active SSH connections (default) or on user-specified clusters.

Key changes:

• New mila run command with parallel execution across multiple clusters
• Automatic detection of active cluster SSH connections
• Rich console output showing results per cluster with color-coded success/failure indicators

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
milatools/cli/run.py	Core implementation of the run command with async execution, cluster detection, and formatted output
milatools/cli/commands.py	Integration of the new run subcommand into the CLI argument parser
tests/cli/test_run.py	Unit tests for the run command logic with mocked RemoteV2 instances
tests/integration/test_run.py	Integration tests that verify the command works with actual SSH connections

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