fix: allow matrix testing without EOL versions (#299)

* fix: remove versions dependent on EOL composer 1

* Restore composer 1 versions

* Add `usable` version type, filtered by code constraints

* Added code comment

* Rebuilt index.js with latest changes merged

* Updated documentation

supported-version/src/kind/get-usable.ts

@@ -0,0 +1,22 @@
+import { PackageMatrixVersion } from '../matrix/matrix-type';
+import { getIndividualVersionsForProject } from "../versions/get-versions-for-project";
+import semver from 'semver';
+
+export const getUsableVersions = (project: string): string[] => {
+    const allVersions = getIndividualVersionsForProject(project)
+    return Object.entries(<Record<string,PackageMatrixVersion>>allVersions)
+        .filter(([key, value]) => {
+            /**
+             * Filter out any versions that are not 'usable', and cannot be successfully installed
+             * anymore for modern systems or other reasons outside our control.
+             */
+
+            // Packagist retired support for Composer 1 on 2025-09-01.
+            if (value.composer && semver.lt(value.composer.toString(), '2.0.0')) {
+                return false;
+            }
+
+            return true;
+        })
+        .map(([key, value]) => key);
+}