services module: move OData filter-schema transformer to a shared utility module

## Context

In `packages/modules/services/src/bookmarks/endpoints/user-bookmarks.get.ts`, the OData filter-schema transformer carries a note that it belongs in a shared location:

```ts
/**
* Schema transformer of the filter object to an OData filter string.
*
* @todo This function should be moved to a shared utility module.
*/
```

## Task

- Identify (or create) an appropriate shared utility module for OData filter-schema transformers within `@equinor/fusion-framework-module-services` (or a more general utils package if it's reusable beyond bookmarks).
- Move the transformer there and update the import in `user-bookmarks.get.ts`.
- Check for other endpoints with similar inline transformers that could reuse the shared utility.

## File

`packages/modules/services/src/bookmarks/endpoints/user-bookmarks.get.ts` (line ~22)

Start with packages/modules/services/src/bookmarks/endpoints/user-bookmarks.get.ts and locate the inline OData filter-schema transformer and its current import context. Inspect the services module or a more general utils package for an appropriate shared location, then check other endpoints for similar transformers. Done means the transformer is shared, user-bookmarks.get.ts uses it, and any suitable duplicate endpoint logic reuses it.

Written by the indexing model from the issue text.