feat: initial working update command

[baszalmstra]

Fixes #73

This PR introduces the pixi update. The update command will update dependencies as recorded in the lock file. The manifest file (pixi.toml/pyproject.toml) itself remains untouched.

Usage: pixi.exe update [OPTIONS] [PACKAGES]...

Arguments:
  [PACKAGES]...  The packages to update

Options:
      --tls-no-verify
          Do not verify the TLS certificate of the server
      --auth-file <AUTH_FILE>
          Path to the file containing the authentication token [env: RATTLER_AUTH_FILE=]
      --pypi-keyring-provider <PYPI_KEYRING_PROVIDER>
          Specifies if we want to use uv keyring provider [possible values: disabled, subprocess]
      --manifest-path <MANIFEST_PATH>
          The path to 'pixi.toml' or 'pyproject.toml'
      --no-install
          Don't modify the environment, only modify the lock-file
  -n, --dry-run
          Don't actually write the lockfile or update any environment
  -e, --env <ENVIRONMENTS>
          The environments to update. If none is specified, all environments are updated
  -p, --platform <PLATFORMS>
          The platforms to update. If none is specified, all platforms are updated
  -v, --verbose...
          Increase logging verbosity
  -q, --quiet...
          Decrease logging verbosity
      --color <COLOR>
          Whether the log needs to be colored [env: PIXI_COLOR=] [default: auto] [possible values: always, never, auto]
      --no-progress
          Hide all progress bars [env: PIXI_NO_PROGRESS=]
  -h, --help
          Print help 

Todo:

• Add tests
• Make sure the output looks correct.
• Update installed environments? Which environment should be updated?

Future work:

• Update PACKAGES... and their dependencies recursively (--recursive).

[jstriebel]

Trying out pixi for more than a simple test for the first time, and was just looking for this 🎉 All the best to the team, props for the very smooth experience so far!!! (PS: We met in Basel)