Automatically close issues/PRs that have been waiting for a reply for too long

# Context

We have too many open issues/PRs and want to automatically close items that are out of date. The simple solution of closing pull requests after a set period of inactivity is hostile to contributors, so we need something more involved.

- [additional reading](https://jacobtomlinson.dev/posts/2024/most-stale-bots-are-anti-user-and-anti-contributor-but-they-dont-have-to-be/)
- https://github.com/ethereum/execution-specs/pull/2408
- https://github.com/ethereum/execution-specs/pull/2470

# Technical

- [ ] Add a new label `S-needs-reply` to the GitHub repository.
- [ ] Add a CI job that removes the `S-needs-reply` label whenever a comment is made or a commit is pushed.
- [ ] Add/modify the stale job to only close issues/PRs with the `S-needs-reply` label.

# Cultural

- Apply the label `S-needs-reply` to issues/PRs that need the original contributor to provide more information or apply code review changes.