Allow pure without purego

### What version of rules_go are you using?

0.48.0

### What version of gazelle are you using?

0.36.0

### What version of Bazel are you using?

bazel 6.4.x

### Does this issue reproduce with the latest releases of all the above?

yes

### What operating system and processor architecture are you using?

Linux

### Any other potentially useful information about your toolchain?

The application is built with `--@io_bazel_rules_go//go/config:pure` to have no dependencies on GLIBC (or any other c library) as this allows building minimal container images.

### What did you do?

Upgraded an application that uses google.golang.org/protobuf to the latest release of rules_go.

### What did you expect to see?

No changes in performance.

### What did you see instead?

The performance of the application has greatly reduced. Enabling "pure" now implies not using pointer arithmetic (https://github.com/search?q=repo%3Aprotocolbuffers%2Fprotobuf-go%20purego&type=code).

While it seems possible to add `gotags` in a `go_binary` it doesn't seem possible to take them away. Using `cgo = False` will still produce a dynamically linked executable (and require glibc at runtime).

Reproduce the application build with rules_go 0.48.0, Gazelle 0.36.0, Bazel 6.4.x, Linux, and the pure configuration. Inspect how the pure setting selects protobuf's purego implementation and how cgo = False affects linking; done means retaining a libc-free executable without the performance regression.

Written by the indexing model from the issue text.