V solutions no longer build

[rbergen]

Both solutions in the V language (as submitted by @marghidanu and @GordonBGood) fail to build since recently, due to a deprecation that apparently should become an error per 01-01-2025, but already causes builds to fail now.

The error reported on PrimeV/solution_1 during CI is as follows:

#13 [build 4/4] RUN v -prod primes.v
#13 0.142 primes.v:28:1: notice: `[attr]` has been deprecated, use `@[attr]` instead
#13 0.142    26 | }
#13 0.142    27 | 
#13 0.142    28 | [direct_array_access]
#13 0.142       | ^
#13 0.142    29 | fn (mut sieve Sieve) run_sieve() {
#13 0.142    30 |     mut factor := u64(3)
#13 0.245 primes.v:4:1: error: const () groups will be an error after 2025-01-01 (`v fmt -w source.v` will fix that for you)
#13 0.245     2 | import math
#13 0.245     3 | 
#13 0.245     4 | const (
#13 0.245       | ~~~~~
#13 0.245     5 |     sieve_size          = 1_000_000
#13 0.245     6 |     q                   = math.sqrt(sieve_size)
#13 ERROR: process "/bin/sh -c v -prod primes.v" did not complete successfully: exit code: 1

I will open a PR to remove the V solutions from the CI and daily benchmark runs, until a PR has been submitted and merged that addresses this problem. I would prefer one PR to address the issue in both solutions, but I will accept single-solution fixes and unblock CI and benchmark runs accordingly.

[rbergen]

@marghidanu provided a proper solution in #982. This issue will be closed when that gets merged.