Support FORCE_COLOR / NO_COLOR env vars

[mjpieters]

Please support the FORCE_COLOR and NO_COLOR environment variables as alternative to the--color CLI switch.

The start-up behaviour then would be:

1. --color set: use this configuration.
2. NO_COLOR set: treat as --color never
3. FORCE_COLOR set: treat as --color always
4. use the default --color auto.

I see typos uses anstyle, like uv, so this is a virtual duplicate of astral-sh/uv#3955, with NO_COLOR already working, and CLICOLOR_FORCE having the same effect as FORCE_COLOR.

[epage]

This is blocked on rust-cli/anstyle#192 as I'm not going to move forward like uv did in astral-sh/uv#3979 due to all of the open question related to FORCE_COLOR (see donatj/force-color.org#30). However, this shouldn't be blocking because CLICOLOR_FORCE exists.

[mjpieters]

My PR interprets FORCE_COLOR the same way CLICOLOR_FORCE is interpreted: as non-empty.