Fix ipv6 validation corner cases

[smaye81]

This ports the ipv6 fix from bufbuild/protovalidate-go#215.

For context see the description on the above PR. The summary is that this fixes the validation for some corner cases of IPv6 address validation. Namely:

• Adds a check that an IPv6 address can't begin or end on a single colon.
• Adds a check to fail-fast on invalid hextets.

[timostamm]

This is a straight port of bufbuild/protovalidate-go#215, right?

Why aren't we removing failing cases from nonconforming.yaml?

[smaye81]

This is a straight port of bufbuild/protovalidate-go#215, right?

Why aren't we removing failing cases from nonconforming.yaml?

It is yeah. We didn't need to add any additional failing cases when we updated to v0.10.4 on main. I guess the validation logic on main correctly handled the new cases added in bufbuild/protovalidate#341.

I didn't add these to the nonconforming.yaml on the sayers/validation_upgrades branch because those new tests actually caused runtime / out-of-range errors when running against the new validation logic. So tl;dr - these tests were never added to nonconforming and this fixes them, so it just evens out.

[timostamm]

those new tests actually caused runtime / out-of-range errors when running against the new validation logic

This means that there are two bugs in that branch:

1. Access out of range on a string.
2. Conformance executor crashing on this exception.

The second bug is fixed by #282.
The first bug is hopefully addressed by this PR.

[smaye81]

The second bug is fixed by #282. The first bug is hopefully addressed by this PR.

It is yeah. You can see the failures in #275, which is 0.10.4 with the ported validation logic but not the fix addressed by this PR.