Fix - program loading with effective slot at epoch boundary (#35283)

* Always limit effective slot to the begin of the current epoch.

* Adds comments.

* Optimizes to avoid having two entries if there is no relevant feature activation.

* Adds test_feature_activation_loaded_programs_epoch_transition().

(cherry picked from commit 2891ce8)

# Conflicts:
#	svm/src/transaction_processor.rs

runtime/src/bank/tests.rs

@@ -11970,6 +11970,60 @@ fn test_feature_activation_loaded_programs_recompilation_phase() {
     );
 }
 
+#[test]
+fn test_feature_activation_loaded_programs_epoch_transition() {
+    solana_logger::setup();
+
+    // Bank Setup
+    let (mut genesis_config, mint_keypair) = create_genesis_config(1_000_000 * LAMPORTS_PER_SOL);
+    genesis_config
+        .accounts
+        .remove(&feature_set::reject_callx_r10::id());
+    let (root_bank, bank_forks) = Bank::new_with_bank_forks_for_tests(&genesis_config);
+
+    // Program Setup
+    let program_keypair = Keypair::new();
+    let program_data = include_bytes!("../../../programs/bpf_loader/test_elfs/out/noop_aligned.so");
+    let program_account = AccountSharedData::from(Account {
+        lamports: Rent::default().minimum_balance(program_data.len()).min(1),
+        data: program_data.to_vec(),
+        owner: bpf_loader::id(),
+        executable: true,
+        rent_epoch: 0,
+    });
+    root_bank.store_account(&program_keypair.pubkey(), &program_account);
+
+    // Compose message using the desired program.
+    let instruction = Instruction::new_with_bytes(program_keypair.pubkey(), &[], Vec::new());
+    let message = Message::new(&[instruction], Some(&mint_keypair.pubkey()));
+    let binding = mint_keypair.insecure_clone();
+    let signers = vec![&binding];
+
+    // Advance the bank so that the program becomes effective.
+    goto_end_of_slot(root_bank.clone());
+    let bank = new_from_parent_with_fork_next_slot(root_bank, bank_forks.as_ref());
+
+    // Load the program with the old environment.
+    let transaction = Transaction::new(&signers, message.clone(), bank.last_blockhash());
+    assert!(bank.process_transaction(&transaction).is_ok());
+
+    // Schedule feature activation to trigger a change of environment at the epoch boundary.
+    let feature_account_balance =
+        std::cmp::max(genesis_config.rent.minimum_balance(Feature::size_of()), 1);
+    bank.store_account(
+        &feature_set::reject_callx_r10::id(),
+        &feature::create_account(&Feature { activated_at: None }, feature_account_balance),
+    );
+
+    // Advance the bank to cross the epoch boundary and activate the feature.
+    goto_end_of_slot(bank.clone());
+    let bank = new_bank_from_parent_with_bank_forks(&bank_forks, bank, &Pubkey::default(), 33);
+
+    // Load the program with the new environment.
+    let transaction = Transaction::new(&signers, message, bank.last_blockhash());
+    assert!(bank.process_transaction(&transaction).is_ok());
+}
+
 #[test]
 fn test_bank_verify_accounts_hash_with_base() {
     let GenesisConfigInfo {