Support getting go version from `toolchain` directive

[ahrtr]

Based on the Getting go version from the go.mod file,

The go directive in go.mod can specify a patch version or omit it altogether (e.g., go 1.22.0 or go 1.22).
If a patch version is specified, that specific patch version will be used.
If no patch version is specified, it will search for the latest available patch version in the cache, 
versions-manifest.json, and the "official Go language website", in that order.

If the go directive doesn't specify a patch version, I think it should use the version specified in toolchain directive (i.e. toolchain go1.23.6) if present. If the toolchain isn't present at all, then you continue to search other options.

[priyagupta108]

Hi @ahrtr 👋,
Thank you for the feature request, we will investigate it and get back to you as soon as we have some feedback.

[mattbnz]

This seems like it duplicates the requests already being discussed in #457 ?