fix: resolve underlying Zig version for Mach builds in anyzls

[kimjune01]

Summary

• Fix crash when anyzls encounters Mach Zig version strings by resolving the underlying Zig version from the index metadata
• Mach versions (e.g., 0.14.0-dev.3163+0) are not valid semver for ZLS compatibility checks; the fix maps them to their base Zig release version

Fixes #73

Test plan

• anyzls no longer crashes when encountering Mach version strings
• Standard semver versions continue to work unchanged

[kimjune01]

Human here. Unfortunate news: I'm moving this into drafts because my current setup uses Zig 0.16 and the build.zig.zon hash format here was authored against an older Zig — I get "invalid hash: incomplete" trying to build locally. I'd need to pin a specific Zig version to validate this fix and I don't have that set up cleanly right now. I wish I could've taken it to completion. Thanks for understanding.

[Verafahn]

Language server zls:

initializing server zls, id 1: Server reset the connection
-- stderr --
anyzig: .mach_zig_version '2026.4.10-mach' pulled from 'E:\Zig\learn-mach\mymach\build.zig.zon'
anyzig: appdata 'C:\Users\lenovo\AppData\Local\anyzig'
anyzig: downloading 'https://builds.zigtools.org/zls-x86_64-windows-0.16.0-dev.3142+5ccfeb926.zip'...
error: bad HTTP response code: '404 Not Found'

The version number format of ZLS is not exactly the same as Zig.

For 2026.4.10-mach. Zig's version number is 0.16.0-dev.3142+5ccfeb926, while ZLS's version number is 0.16.0-dev.300+f391142c.

Perhaps the corresponding version number of ZLS can be obtained by crawling data from https://zigtools.org/zls/?zig_version=<zig version>&compatibility=only-runtime.

[Verafahn]

The API that can be used to request ZLS version is https://releases.zigtools.org/v1/zls/select-version?zig_version=0.16.0&compatibility=only-runtime