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/http_api/tests/tests.rs

@@ -178,6 +178,9 @@ impl ApiTester {
             "precondition: current slot is one after head"
         );
 
+        // Set a min blob count for the next block for get_blobs testing
+        harness.execution_block_generator().set_min_blob_count(2);
+
         let (next_block, _next_state) = harness
             .make_block(head.beacon_state.clone(), harness.chain.slot().unwrap())
             .await;
@@ -1869,7 +1872,7 @@ impl ApiTester {
     }
 
     pub async fn test_get_blob_sidecars(self, use_indices: bool) -> Self {
-        let block_id = BlockId(CoreBlockId::Finalized);
+        let block_id = BlockId(CoreBlockId::Head);
         let (block_root, _, _) = block_id.root(&self.chain).unwrap();
         let (block, _, _) = block_id.full_block(&self.chain).await.unwrap();
         let num_blobs = block.num_expected_blobs();
@@ -1902,7 +1905,7 @@ impl ApiTester {
     }
 
     pub async fn test_get_blobs(self, versioned_hashes: bool) -> Self {
-        let block_id = BlockId(CoreBlockId::Finalized);
+        let block_id = BlockId(CoreBlockId::Head);
         let (block_root, _, _) = block_id.root(&self.chain).unwrap();
         let (block, _, _) = block_id.full_block(&self.chain).await.unwrap();
         let num_blobs = block.num_expected_blobs();
@@ -1940,7 +1943,7 @@ impl ApiTester {
     }
 
     pub async fn test_get_blobs_post_fulu_full_node(self, versioned_hashes: bool) -> Self {
-        let block_id = BlockId(CoreBlockId::Finalized);
+        let block_id = BlockId(CoreBlockId::Head);
         let (block_root, _, _) = block_id.root(&self.chain).unwrap();
         let (block, _, _) = block_id.full_block(&self.chain).await.unwrap();
 
@@ -7867,6 +7870,8 @@ async fn get_blobs_post_fulu_supernode() {
     config.spec.fulu_fork_epoch = Some(Epoch::new(0));
 
     ApiTester::new_from_config(config)
+        .await
+        .test_post_beacon_blocks_valid()
         .await
         // We can call the same get_blobs function in this test
         // because the function will call get_blobs_by_versioned_hashes which handles peerDAS post-Fulu
@@ -7887,6 +7892,8 @@ async fn get_blobs_post_fulu_full_node() {
     config.spec.fulu_fork_epoch = Some(Epoch::new(0));
 
     ApiTester::new_from_config(config)
+        .await
+        .test_post_beacon_blocks_valid()
         .await
         .test_get_blobs_post_fulu_full_node(false)
         .await