Proposal: mark all versions of Rust packages deprecated for RUSTSEC "unmaintained" advisories

The Rust community creates RUSTSEC advisories when a package is considered unmaintained. These are indicated by adding `”informational”: “unmaintained”` to the `database_specific` field in the OSV schema. For example: [RUSTSEC-2025-0141](https://osv.dev/vulnerability/RUSTSEC-2025-0141). While deps.dev will indicate the presence of this advisory, it does not flag the package as deprecated.

I propose that deps.dev use the presence of this entry on an advisory to set `"isDeprecated": true` on all versions of the package. This more clearly indicates the intent of these advisories: that the package has a _potential_ security risk, not that it contains a _current_ vulnerability.

No file or test is named. Start by locating where deps.dev ingests OSV advisories and determines package-version deprecation, then trace how RUSTSEC metadata reaches the API. Done means an advisory with database_specific informational set to unmaintained marks every package version as isDeprecated without treating it as a current vulnerability.

Written by the indexing model from the issue text.