Reduce number of blobs used in tests to speed up CI (#8194)

`beacon-chain-tests` is now regularly taking 1h+ on CI since Fulu fork was added.

This PR attemtpts to reduce the test time by bringing down the number of blobs generated in tests - instead of generating 0..max_blobs, the generator now generates 0..1 blobs by default, and this can be modified by setting `harness.execution_block_generator.set_min_blob_count(n)`.

Note: The blobs are pre-generated and doesn't require too much CPU to generate however processing a larger number of them on the beacon chain does take a lot of time.

This PR also include a few other small improvements
- Our slowest test (`chain_segment_varying_chunk_size`) runs 3x faster in Fulu just by reusing chain segments
- Avoid re-running fork specific tests on all forks
- Fix a bunch of tests that depends on the harness's existing random blob generation, which is fragile


beacon chain test time on test machine is **~2x** faster:

### `unstable`

```
Summary [ 751.586s] 291 tests run: 291 passed (13 slow), 0 skipped
```

### this branch

```
Summary [ 373.792s] 291 tests run: 291 passed (2 slow), 0 skipped
```

The next set of tests to optimise is the ones that use [`get_chain_segment`](77a9af96de/beacon_node/beacon_chain/tests/block_verification.rs (L45)), as it by default build 320 blocks with supernode - an easy optimisation would be to build these blocks with cgc = 8 for tests that only require fullnodes.


  


Co-Authored-By: Jimmy Chen <jchen.tc@gmail.com>

Co-Authored-By: Jimmy Chen <jimmy@sigmaprime.io>

beacon_node/beacon_chain/tests/events.rs

@@ -1,20 +1,26 @@
 use beacon_chain::blob_verification::GossipVerifiedBlob;
 use beacon_chain::data_column_verification::GossipVerifiedDataColumn;
-use beacon_chain::test_utils::{BeaconChainHarness, generate_data_column_sidecars_from_block};
+use beacon_chain::test_utils::{
+    BeaconChainHarness, fork_name_from_env, generate_data_column_sidecars_from_block, test_spec,
+};
 use eth2::types::{EventKind, SseBlobSidecar, SseDataColumnSidecar};
 use rand::SeedableRng;
 use rand::rngs::StdRng;
 use std::sync::Arc;
 use types::blob_sidecar::FixedBlobSidecarList;
 use types::test_utils::TestRandom;
-use types::{BlobSidecar, DataColumnSidecar, EthSpec, ForkName, MinimalEthSpec, Slot};
+use types::{BlobSidecar, DataColumnSidecar, EthSpec, MinimalEthSpec, Slot};
 
 type E = MinimalEthSpec;
 
 /// Verifies that a blob event is emitted when a gossip verified blob is received via gossip or the publish block API.
 #[tokio::test]
 async fn blob_sidecar_event_on_process_gossip_blob() {
-    let spec = Arc::new(ForkName::Deneb.make_genesis_spec(E::default_spec()));
+    if fork_name_from_env().is_some_and(|f| !f.deneb_enabled() || f.fulu_enabled()) {
+        return;
+    };
+
+    let spec = Arc::new(test_spec::<E>());
     let harness = BeaconChainHarness::builder(E::default())
         .spec(spec)
         .deterministic_keypairs(8)
@@ -48,7 +54,11 @@ async fn blob_sidecar_event_on_process_gossip_blob() {
 /// Verifies that a data column event is emitted when a gossip verified data column is received via gossip or the publish block API.
 #[tokio::test]
 async fn data_column_sidecar_event_on_process_gossip_data_column() {
-    let spec = Arc::new(ForkName::Fulu.make_genesis_spec(E::default_spec()));
+    if fork_name_from_env().is_some_and(|f| !f.fulu_enabled()) {
+        return;
+    };
+
+    let spec = Arc::new(test_spec::<E>());
     let harness = BeaconChainHarness::builder(E::default())
         .spec(spec)
         .deterministic_keypairs(8)
@@ -93,7 +103,11 @@ async fn data_column_sidecar_event_on_process_gossip_data_column() {
 /// Verifies that a blob event is emitted when blobs are received via RPC.
 #[tokio::test]
 async fn blob_sidecar_event_on_process_rpc_blobs() {
-    let spec = Arc::new(ForkName::Deneb.make_genesis_spec(E::default_spec()));
+    if fork_name_from_env().is_some_and(|f| !f.deneb_enabled() || f.fulu_enabled()) {
+        return;
+    };
+
+    let spec = Arc::new(test_spec::<E>());
     let harness = BeaconChainHarness::builder(E::default())
         .spec(spec)
         .deterministic_keypairs(8)
@@ -112,7 +126,7 @@ async fn blob_sidecar_event_on_process_rpc_blobs() {
     let slot = head_state.slot() + 1;
     let ((signed_block, opt_blobs), _) = harness.make_block(head_state, slot).await;
     let (kzg_proofs, blobs) = opt_blobs.unwrap();
-    assert!(blobs.len() > 2);
+    assert_eq!(blobs.len(), 2);
 
     let blob_1 =
         Arc::new(BlobSidecar::new(0, blobs[0].clone(), &signed_block, kzg_proofs[0]).unwrap());
@@ -144,7 +158,11 @@ async fn blob_sidecar_event_on_process_rpc_blobs() {
 
 #[tokio::test]
 async fn data_column_sidecar_event_on_process_rpc_columns() {
-    let spec = Arc::new(ForkName::Fulu.make_genesis_spec(E::default_spec()));
+    if fork_name_from_env().is_some_and(|f| !f.fulu_enabled()) {
+        return;
+    };
+
+    let spec = Arc::new(test_spec::<E>());
     let harness = BeaconChainHarness::builder(E::default())
         .spec(spec.clone())
         .deterministic_keypairs(8)