Claiming namespace plum-lang

### Namespace

plum-lang

### Ownership

- [ ] The namespace is not currently owned on Open VSX (verify by a search on [open-vsx.org](https://open-vsx.org))

### Account Age

- [ ] The GitHub ID making this request has at least 12 months of public history

### VS Code Publisher with Repo

- [x] The namespace is also a publisher account on the VS Code Marketplace (check by browsing https://marketplace.visualstudio.com/publishers/{publisher}) and has an extension published there with a repo specified in its package.json file.

### VS Code Publisher without Repo

- [ ] The namespace is also a publisher account on the VS Code Marketplace and does not have published extensions or has published extensions with no GitHub repos.

### Not a VS Code Marketplace Publisher

- [ ] The namespace is not a publisher account on the VS Code Marketplace

### All Other Cases

- [ ] You are unable to provide the inputs required in the three options above. This option will take the longest to process.

### Claim evidence

Provide the requested information (commit URL or domain/subdomain) or a justification for granting ownership of the namespace.

Verify the plum-lang namespace on open-vsx.org, confirm the GitHub account's public history, and check the corresponding VS Code Marketplace publisher and repository information. The request is complete when the required claim evidence is provided and the namespace ownership decision can be processed.

Written by the indexing model from the issue text.