Add support for loading keypairs from file

eth2/state_processing/benches/bench_epoch_processing.rs

@@ -10,6 +10,7 @@ use state_processing::{
         update_latest_slashed_balances,
     },
 };
+use std::path::Path;
 use types::test_utils::TestingBeaconStateBuilder;
 use types::{validator_registry::get_active_validator_indices, *};
 
@@ -17,10 +18,14 @@ pub const BENCHING_SAMPLE_SIZE: usize = 10;
 pub const SMALL_BENCHING_SAMPLE_SIZE: usize = 10;
 
 /// Run the benchmarking suite on a foundation spec with 16,384 validators.
-pub fn bench_epoch_processing_n_validators(c: &mut Criterion, validator_count: usize) {
+pub fn bench_epoch_processing_n_validators(
+    c: &mut Criterion,
+    validator_count: usize,
+    keypair_file: Option<&Path>,
+) {
     let spec = ChainSpec::foundation();
 
-    let mut builder = TestingBeaconStateBuilder::new(validator_count, &spec);
+    let mut builder = TestingBeaconStateBuilder::new(validator_count, keypair_file, &spec);
 
     // Set the state to be just before an epoch transition.
     let target_slot = (spec.genesis_epoch + 4).end_slot(spec.slots_per_epoch);