x.chacha: fix overflow

[kbkpbot]

1. Fix CI problem cause by u64(1 << 63) -1, https://github.com/vlang/v/actions/runs/14119063556/job/39555765325?pr=24059
2. support full range of 64bit counter
3. add tests

TODO:

1. Add assembly version for amd64 , arm64
2. more checks for boundary condition, such as when counter got a value of 0xffff_ffff_ffff_ffff

[huly-for-github]

Connected to Huly®: V_0.6-22455

[spytheman]

Excellent work.
Thank you 🙇🏻‍♂️ .

[blackshirt]

Thank you @kbkpbot for the fix. Generally speaking, i think the x.crypto.chacha20 module overall is in a good state, but, 64-bit counter variant was still need more testing throughly.