refactor: remove unnecessary optimization infrastructure

Keep only the essential fix for redundant client-side filtering.
The optimization infrastructure was over-engineered for a problem
that doesn't really exist - the GraphQL API already supports
server-side filtering properly.

Author: sapientpants

.changeset/fix-redundant-filtering.md

@@ -0,0 +1,10 @@
+---
+'deepsource-mcp-server': patch
+---
+
+fix: remove redundant client-side filtering in quality metrics handler
+
+The quality metrics handler was unnecessarily filtering metrics on the client side
+after the GraphQL API had already applied the same filters on the server side.
+This change removes the redundant filtering by using the repository's
+findByProjectWithFilter method when shortcode filters are specified.