Implement basic validator custody framework (no backfill) (#7578)

Resolves #6767


  This PR implements a basic version of validator custody.
- It introduces a new `CustodyContext` object which contains info regarding number of validators attached to a node and  the custody count they contribute to the cgc.
- The `CustodyContext` is added in the da_checker and has methods for returning the current cgc and the number of columns to sample at head. Note that the logic for returning the cgc existed previously in the network globals.
- To estimate the number of validators attached, we use the `beacon_committee_subscriptions` endpoint. This might overestimate the number of validators actually publishing attestations from the node in the case of multi BN setups. We could also potentially use the `publish_attestations` endpoint to get a more conservative estimate at a later point.
- Anytime there's a change in the `custody_group_count` due to addition/removal of validators, the custody context should send an event on a broadcast channnel. The only subscriber for the channel exists in the network service which simply subscribes to more subnets. There can be additional subscribers in sync that will start a backfill once the cgc changes.

TODO

- [ ] **NOT REQUIRED:** Currently, the logic only handles an increase in validator count and does not handle a decrease. We should ideally unsubscribe from subnets when the cgc has decreased.
- [ ] **NOT REQUIRED:** Add a service in the `CustodyContext` that emits an event once `MIN_EPOCHS_FOR_BLOB_SIDECARS_REQUESTS ` passes after updating the current cgc. This event should be picked up by a subscriber which updates the enr and metadata.
- [x] Add more tests

consensus/types/src/chain_spec.rs

@@ -203,6 +203,8 @@ pub struct ChainSpec {
     pub data_column_sidecar_subnet_count: u64,
     pub samples_per_slot: u64,
     pub custody_requirement: u64,
+    pub validator_custody_requirement: u64,
+    pub balance_per_additional_custody_group: u64,
 
     /*
      * Networking
@@ -731,14 +733,6 @@ impl ChainSpec {
         Ok(std::cmp::max(custody_column_count, self.samples_per_slot))
     }
 
-    pub fn custody_group_count(&self, is_supernode: bool) -> u64 {
-        if is_supernode {
-            self.number_of_custody_groups
-        } else {
-            self.custody_requirement
-        }
-    }
-
     pub fn all_data_column_sidecar_subnets(&self) -> impl Iterator<Item = DataColumnSubnetId> {
         (0..self.data_column_sidecar_subnet_count).map(DataColumnSubnetId::new)
     }
@@ -975,6 +969,8 @@ impl ChainSpec {
             data_column_sidecar_subnet_count: 128,
             number_of_columns: 128,
             samples_per_slot: 8,
+            validator_custody_requirement: 8,
+            balance_per_additional_custody_group: 32000000000,
 
             /*
              * Network specific
@@ -1309,6 +1305,8 @@ impl ChainSpec {
             data_column_sidecar_subnet_count: 128,
             number_of_columns: 128,
             samples_per_slot: 8,
+            validator_custody_requirement: 8,
+            balance_per_additional_custody_group: 32000000000,
 
             /*
              * Network specific
@@ -1650,6 +1648,12 @@ pub struct Config {
     #[serde(default = "BlobSchedule::default")]
     #[serde(skip_serializing_if = "BlobSchedule::is_empty")]
     blob_schedule: BlobSchedule,
+    #[serde(default = "default_validator_custody_requirement")]
+    #[serde(with = "serde_utils::quoted_u64")]
+    validator_custody_requirement: u64,
+    #[serde(default = "default_balance_per_additional_custody_group")]
+    #[serde(with = "serde_utils::quoted_u64")]
+    balance_per_additional_custody_group: u64,
 }
 
 fn default_bellatrix_fork_version() -> [u8; 4] {
@@ -1815,6 +1819,14 @@ const fn default_samples_per_slot() -> u64 {
     8
 }
 
+const fn default_validator_custody_requirement() -> u64 {
+    8
+}
+
+const fn default_balance_per_additional_custody_group() -> u64 {
+    32000000000
+}
+
 fn max_blocks_by_root_request_common(max_request_blocks: u64) -> usize {
     let max_request_blocks = max_request_blocks as usize;
     RuntimeVariableList::<Hash256>::from_vec(
@@ -2024,6 +2036,8 @@ impl Config {
             samples_per_slot: spec.samples_per_slot,
             custody_requirement: spec.custody_requirement,
             blob_schedule: spec.blob_schedule.clone(),
+            validator_custody_requirement: spec.validator_custody_requirement,
+            balance_per_additional_custody_group: spec.balance_per_additional_custody_group,
         }
     }
 
@@ -2103,6 +2117,8 @@ impl Config {
             samples_per_slot,
             custody_requirement,
             ref blob_schedule,
+            validator_custody_requirement,
+            balance_per_additional_custody_group,
         } = self;
 
         if preset_base != E::spec_name().to_string().as_str() {
@@ -2187,6 +2203,8 @@ impl Config {
             samples_per_slot,
             custody_requirement,
             blob_schedule: blob_schedule.clone(),
+            validator_custody_requirement,
+            balance_per_additional_custody_group,
 
             ..chain_spec.clone()
         })