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/network/src/sync/block_sidecar_coupling.rs

@@ -517,11 +517,10 @@ mod tests {
 
     #[test]
     fn no_blobs_into_responses() {
-        let spec = test_spec::<E>();
         let mut rng = XorShiftRng::from_seed([42; 16]);
         let blocks = (0..4)
             .map(|_| {
-                generate_rand_block_and_blobs::<E>(ForkName::Base, NumBlobs::None, &mut rng, &spec)
+                generate_rand_block_and_blobs::<E>(ForkName::Base, NumBlobs::None, &mut rng)
                     .0
                     .into()
             })
@@ -540,19 +539,13 @@ mod tests {
 
     #[test]
     fn empty_blobs_into_responses() {
-        let spec = test_spec::<E>();
         let mut rng = XorShiftRng::from_seed([42; 16]);
         let blocks = (0..4)
             .map(|_| {
                 // Always generate some blobs.
-                generate_rand_block_and_blobs::<E>(
-                    ForkName::Deneb,
-                    NumBlobs::Number(3),
-                    &mut rng,
-                    &spec,
-                )
-                .0
-                .into()
+                generate_rand_block_and_blobs::<E>(ForkName::Deneb, NumBlobs::Number(3), &mut rng)
+                    .0
+                    .into()
             })
             .collect::<Vec<Arc<SignedBeaconBlock<E>>>>();
 

beacon_node/network/src/sync/tests/lookups.rs

@@ -194,7 +194,7 @@ impl TestRig {
     ) -> (SignedBeaconBlock<E>, Vec<BlobSidecar<E>>) {
         let fork_name = self.fork_name;
         let rng = &mut self.rng;
-        generate_rand_block_and_blobs::<E>(fork_name, num_blobs, rng, &self.spec)
+        generate_rand_block_and_blobs::<E>(fork_name, num_blobs, rng)
     }
 
     fn rand_block_and_data_columns(
@@ -1146,10 +1146,8 @@ impl TestRig {
 
 #[test]
 fn stable_rng() {
-    let spec = types::MainnetEthSpec::default_spec();
     let mut rng = XorShiftRng::from_seed([42; 16]);
-    let (block, _) =
-        generate_rand_block_and_blobs::<E>(ForkName::Base, NumBlobs::None, &mut rng, &spec);
+    let (block, _) = generate_rand_block_and_blobs::<E>(ForkName::Base, NumBlobs::None, &mut rng);
     assert_eq!(
         block.canonical_root(),
         Hash256::from_slice(