tezos-stdlib-unix: add domain-name conflict

[mseri]

It currently uses fmt, which is obtained transitively via some dependency which, in turns, depends on domain-name-conflict.

Seen on: #19881 (comment)

[mseri]

Indeed, thanks a lot!

[mseri]

Thanks

[kit-ty-kate]

I don't understand this PR. What was the original issue?

[hannesm]

The original issue unfolds as follows:

• domain-name 0.3.1 was released (in [new release] domain-name (0.3.1) #19881) which dropped depeendencies on fmt and astring
• tezos* failed since it uses "fmt" (missing in opam dependencies, and also in the dune file) -- this was implicitly present by ipaddr depending on domain-name, and tezos-stdlib-unix depending on ipaddr.
• while CI was running, further missing lower bounds were detected (ezjsonm / fmt)