Docker v26 compatibility & test fixes

[apostasie]

This fix #3088

So far, the issues were:

• [x] docker is now pickier on ip ranges
• [x] WithMacAddress: both host networking and container networking now apparently allow passing a mac address, though it is a no-op AFAIK - the docker daemon still disallows it - hypothesis is that the new cli just discard the option silently. Anyhow, nerdctl code has been changed to align with that (somewhat abhorrent) behavior and tests have been adjusted
• [x] TestRunContainerWithStaticIP: see #3101 - I am disabling the test for now (which was already broken by the way, since it wasn't testing anything for docker) - we might re-enable pending discussion in the linked ticket

[apostasie]

Besides a Windows failure that seems unrelated (can you poke it?), the CI is green on this.

As indicated in the initial comment, issues are relatively minor changes in behavior of the docker cli, that we are now aligning with, for better or worse (except for the behavior on ip + bridge which is now documented in #3106).

Tests have also been cleaned up slightly as some assumptions were wrong (availability of /sys/net, and multiple execution through testutil assert helpers), the logic has been simplified a bit, and they are now parallelized.

@AkihiroSuda and crew, PTAL at your convenience.