[Feature Request] Create git tags for the `pkg/parser` sub-module

Hi TiDB Team,

We are using [github.com/pingcap/tidb/pkg/parser](https://github.com/pingcap/tidb/tree/master/pkg/parser) as a standalone Go module dependency in our project. Currently, the repository root maintains release tags (e.g., `v8.5.4`), but there are no corresponding module-prefixed tags created for the `pkg/parser` sub-module directory.

According to the official Go documentation on [sourcing multiple modules in a single repository](https://go.dev/doc/modules/managing-source#multiple-module-source), sub-modules located in subdirectories require tags prefixed with the relative directory path to allow Go toolchains and module proxies to index and resolve specific versions correctly (e.g., `pkg/parser/v1.x.x`).

### Proposed Solution

Could you please add git tags prefixed with `pkg/parser/` whenever it was changed ?

For example:

```shell
git tag pkg/parser/v1.2.3
git push origin pkg/parser/v1.2.3
```

This would significantly improve dependency management, caching, and deterministic version locking for downstream projects relying directly on [github.com/pingcap/tidb/pkg/parser](https://github.com/pingcap/tidb/tree/master/pkg/parser).

Thank you for your time and help!

---

Start by inspecting the existing release process and root version tags, then verify how the pkg/parser sub-module is defined and detected when it changes. Confirm the required Go module tag format and determine how tags are created and pushed. Done means parser changes produce correctly prefixed pkg/parser/v* tags that Go tooling can resolve.

Written by the indexing model from the issue text.