Add Atomic BlockState Snapshot to Prevent Race Conditions

Summary

This PR introduces an atomic BlockState snapshot mechanism in the UTXO store to prevent race conditions between block height and median block time reads during transaction validation.

Problem

Previously, GetBlockHeight() and GetMedianBlockTime() were called separately during validation. This created a race condition where:

• Block height could be read
• Block state updates in between
• Median block time read reflects a different state
• This inconsistency could cause validation errors or incorrect finality checks

Solution

Introduced GetBlockState() method that returns an atomic snapshot containing both:

type BlockState struct {
    Height     uint32 // Current block height
    MedianTime uint32 // Median time of recent blocks
}

Changes

• stores/utxo/Interface.go: Added BlockState struct and GetBlockState() interface method
• stores/utxo/mock.go: Implemented mock for GetBlockState()
• stores/utxo/aerospike|sql|nullstore: Implemented GetBlockState() in all store implementations
• services/validator/Validator.go: Updated validation logic to use atomic GetBlockState() instead of separate calls
• All test files: Updated mocks to use GetBlockState() instead of deprecated separate calls

Benefits

• ✅ Eliminates race conditions during concurrent block state updates
• ✅ Ensures consistency between height and median time during validation
• ✅ Improves reliability of transaction finality checks (BIP113)
• ✅ Cleaner API with single atomic operation

Testing

• Updated all existing tests to use new GetBlockState() mock
• All validator tests pass with the new atomic snapshot approach