Drop 0.14 and 0.15

[AlbertShown]

Zig 0.14 and 0.15 can't be built with latest macOS XCode 26.6. Instead of downgrade XCode to old 26.3 I prefer to drop the old Zig versions.

Info:

https://github.com/webui-dev/webui/actions/runs/29778394681/job/88473330218

https://codeberg.org/ziglang/zig/issues/31658

[AlbertShown]

A big one single PR is done 8d6bc9b .

Basically, we dropped 0.14 and 0.15 as we need to do it anyway one day. Now we only support +0.16.

The repo version is standardized to 2.5.x (2.5.1) to match all other wrappers format.

However, we can still create a branch with old 0.14 and 0.15 commits if people still use old Zig for any reason.

I tested all examples, they are all working great!

@jinzhongjia

[jinzhongjia]

OK, I get it

[jinzhongjia]

I should have some free time this week or next weekend to handle a few issues.