Implement inactivity scores ef tests unstable (#8807)

fixes issue #8750


  This PR enables the inactivity_scores reward EF tests from v1.7.0-alpha.2.

- Enabled Tests: Added the inactivity_scores handler to the rewards test suite.
- Fork Filtering: Updated the runner to execute these tests only on supported forks (Altair onwards), preventing directory-not-found errors on earlier forks.
- CI Coverage: Removed exclusions in the file access check script to ensures all new test vectors are fully tracked.


Co-Authored-By: romeoscript <romeobourne211@gmail.com>

Co-Authored-By: Eitan Seri-Levi <eserilev@gmail.com>

Co-Authored-By: Michael Sproul <michael@sigmaprime.io>

testing/ef_tests/tests/tests.rs

@@ -1113,7 +1113,7 @@ fn kzg_inclusion_merkle_proof_validity() {
 
 #[test]
 fn rewards() {
-    for handler in &["basic", "leak", "random"] {
+    for handler in &["basic", "leak", "random", "inactivity_scores"] {
         RewardsHandler::<MinimalEthSpec>::new(handler).run();
         RewardsHandler::<MainnetEthSpec>::new(handler).run();
     }