fix: ensure unique epochs in BlobSchedule initialization

[CertiK-Geth]

Issue Addressed

#8400

Proposed Changes

1. consensus/types/src/chain_spec.rs - BlobSchedule::new() Method

Change: Modified to return Result<Self, String> and validate epoch uniqueness.

Before:

pub fn new(mut vec: Vec<BlobParameters>) -> Self {
    // reverse sort by epoch
    vec.sort_by(|a, b| b.epoch.cmp(&a.epoch));
    Self {
        schedule: vec,
        skip_serializing: false,
    }
}

After:

pub fn new(mut vec: Vec<BlobParameters>) -> Result<Self, String> {
    // reverse sort by epoch
    vec.sort_by(|a, b| b.epoch.cmp(&a.epoch));
    
    // Validate that all epochs are unique
    for i in 0..vec.len() {
        for j in (i + 1)..vec.len() {
            if vec[i].epoch == vec[j].epoch {
                return Err(format!(
                    "Duplicate epoch in blob schedule: epoch {}",
                    vec[i].epoch
                ));
            }
        }
    }
    
    Ok(Self {
        schedule: vec,
        skip_serializing: false,
    })
}

2. consensus/types/src/chain_spec.rs - Deserialize Implementation

Change: Updated to properly handle and propagate validation errors from BlobSchedule::new().

Before:

impl<'de> Deserialize<'de> for BlobSchedule {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: Deserializer<'de>,
    {
        let vec = Vec::<BlobParameters>::deserialize(deserializer)?;
        Ok(BlobSchedule::new(vec))
    }
}

After:

impl<'de> Deserialize<'de> for BlobSchedule {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: Deserializer<'de>,
    {
        let vec = Vec::<BlobParameters>::deserialize(deserializer)?;
        BlobSchedule::new(vec).map_err(serde::de::Error::custom)
    }
}

3. consensus/types/src/chain_spec.rs - mainnet() Method

Change: Updated to handle the Result return type from BlobSchedule::new().

Before:

blob_schedule: BlobSchedule::new(vec![
    BlobParameters {
        epoch: Epoch::new(412672),
        max_blobs_per_block: 15,
    },
    BlobParameters {
        epoch: Epoch::new(419072),
        max_blobs_per_block: 21,
    },
]),

After:

blob_schedule: BlobSchedule::new(vec![
    BlobParameters {
        epoch: Epoch::new(412672),
        max_blobs_per_block: 15,
    },
    BlobParameters {
        epoch: Epoch::new(419072),
        max_blobs_per_block: 21,
    },
])
.expect("mainnet blob schedule has unique epochs"),

4. consensus/types/src/fork_context.rs - Test Helper

Change: Updated the test helper make_chain_spec() to handle the Result return type.

Before:

spec.blob_schedule = BlobSchedule::new(blob_parameters);

After:

spec.blob_schedule = BlobSchedule::new(blob_parameters)
    .expect("test blob schedule has unique epochs");

5. Added Comprehensive Test Suite

Added blob_schedule_tests module with 4 tests:

• test_unique_epochs_accepted() - Verifies that valid schedules with unique epochs are accepted
• test_duplicate_epochs_rejected() - Verifies that schedules with duplicate epochs are rejected with proper error message
• test_empty_schedule() - Verifies that empty schedules are accepted
• test_single_entry() - Verifies that single-entry schedules are accepted

Additional Info

1. ✅ Config deserialization properly validates blob schedule uniqueness
2. ✅ Duplicate epochs are detected and rejected with clear error messages
3. ✅ Valid configurations pass without issue
4. ✅ Edge cases (empty, single entry) are handled correctly
5. ✅ Existing code paths that hardcode valid blob schedules continue to work

[cla-assistant]

All committers have signed the CLA.