**What type of PR is this?**

Bug fix

**What does this PR do? Why is it needed?**
I'm trying to use an extension-generated repo as a wrapped sdk using
`root_files`. I get a package load error similar to
bazelbuild/bazel#19301.

**Which issues(s) does this PR fix?**
I saw in the comments (specifically
bazelbuild/bazel#19301 (comment))
that this would probably work if `root_files` used a
`string_keyed_label_dict` and, when I tried it locally it did.

Fixes #4418

**Other notes for review**
bazelbuild/bazel#19301

**What type of PR is this?**

Bug fix

**What does this PR do? Why is it needed?**

After #4402, it is no longer possible to use a custom analyzer without
having to declare a new `Fact` type. The build of a Go library will fail
if the library contains any external dependencies.

That's the case for executing gazelle by example (if we don't use a
precompiled binary):

```
$ bazel run //:gazelle
ERROR: .../external/gazelle++go_deps+org_golang_x_sync/errgroup/BUILD.bazel:3:11: output 'external/gazelle++go_deps+org_golang_x_sync/errgroup/errgroup.facts' was not created
ERROR: .../external/gazelle++go_deps+org_golang_x_sync/errgroup/BUILD.bazel:3:11: Running nogo on @@gazelle++go_deps+org_golang_x_sync//errgroup:errgroup failed: not all outputs were created or valid
ERROR: .../external/gazelle++go_deps+com_github_bazelbuild_buildtools/labels/BUILD.bazel:3:11: output 'external/gazelle++go_deps+com_github_bazelbuild_buildtools/labels/labels.facts' was not created
ERROR: .../external/gazelle++go_deps+com_github_bazelbuild_buildtools/labels/BUILD.bazel:3:11: Running nogo on @@gazelle++go_deps+com_github_bazelbuild_buildtools//labels:labels failed: not all outputs were created or valid
ERROR: .../external/gazelle++go_deps+in_gopkg_yaml_v3/BUILD.bazel:5:11: output 'external/gazelle++go_deps+in_gopkg_yaml_v3/yaml_v3.facts' was not created
ERROR: .../external/gazelle++go_deps+in_gopkg_yaml_v3/BUILD.bazel:5:11: Running nogo on @@gazelle++go_deps+in_gopkg_yaml_v3//:yaml_v3 failed: not all outputs were created or valid
ERROR: .../external/gazelle++go_deps+org_golang_x_sys/execabs/BUILD.bazel:3:11: output 'external/gazelle++go_deps+org_golang_x_sys/execabs/execabs.facts' was not created
ERROR: .../external/gazelle++go_deps+org_golang_x_sys/execabs/BUILD.bazel:3:11: Running nogo on @@gazelle++go_deps+org_golang_x_sys//execabs:execabs failed: not all outputs were created or valid
...
```

**Other notes for review**

This review continue to skip analysers when ignoring diagnostics, but
return a valid `pkg` to create the missing `.facts` file required by the
validation action, and incidentally, fix a potential crash at line
https://github.com/bazel-contrib/rules_go/blob/1f993522f463c142c5516f94852c3d6597f717c6/go/tools/builders/nogo_main.go#L98.

A “deprecated” comment must be a separate paragraph, and there must be
at least one other paragraph in the docstring. Otherwise pkg.go.dev
won’t mark the symbol as deprecated.

**What type of PR is this?**

Documentation

**What does this PR do? Why is it needed?**

Correctly marks the deprecated symbols as deprecated on pkg.go.dev.

**Which issues(s) does this PR fix?**

Fixes #

**Other notes for review**

**What type of PR is this?**

Fix for compatibility with Go 1.25

**What does this PR do? Why is it needed?**

The `pack` command, which is no longer shipped as a prebuilt binary with
Go 1.25, is now compiled from source together with the `builder` binary.

Conditional logic is avoided by always compiling `pack` from source,
even on Go versions before 1.25. By enabling `go build` caching in
`go_tool_binary`, the overhead compared to building just the `builder`
binary is negligible.

**Which issues(s) does this PR fix?**

ref: golang/go#74080
fixes #4398

**Other notes for review**

---------

Co-authored-by: rhang <rhang@uber.com>

**What type of PR is this?**

Feature

**What does this PR do? Why is it needed?**

**Which issues(s) does this PR fix?**

**Other notes for review**


https://bazelbuild.slack.com/archives/CDBP88Z0D/p1751654245992999?thread_ts=1751654245.992999&cid=CDBP88Z0D