Implement standardized JSON format for slow block logging to enable
cross-client performance analysis and protocol research.

This change is part of the Cross-Client Execution Metrics initiative
proposed by Gary Rong: https://hackmd.io/dg7rizTyTXuCf2LSa2LsyQ

The standardized metrics enabled data-driven analysis like the EIP-7907
research: https://ethresear.ch/t/data-driven-analysis-on-eip-7907/23850

JSON format includes:
- block: number, hash, gas_used, tx_count
- timing: execution_ms, total_ms
- throughput: mgas_per_sec
- state_reads: accounts, storage_slots, code, code_bytes
- state_writes: accounts, storage_slots
- cache: account/storage/code hits, misses, hit_rate

Convert timing parameters from u64 to f64 to preserve sub-millisecond
precision in slow block JSON output.

Changes:
- log_slow_block() timing params: u64 -> f64
- is_slow_block(): u64 -> f64 with threshold cast
- Tracing format: add {:.3} for 3 decimal places
- Update tests for f64 values

Add tracking for EIP-7702 delegation set/cleared operations as part of
the cross-client execution metrics standardization effort.

New parameters in log_slow_block():
- eip7702_delegations_set: Number of EIP-7702 delegations set
- eip7702_delegations_cleared: Number of EIP-7702 delegations cleared

These fields will be 0 for pre-Pectra blocks per spec.

Add core infrastructure for tracking block execution metrics:
- ExecutionStats struct with state reads/writes/cache fields
- EIP-7702 delegation counters
- Timing breakdown (execution, state_read, state_hash, commit)

Wire ExecutionStats collection into the engine tree:
- Add instrumented state wrapper for metrics capture
- Integrate with payload validation pipeline
- Add slow block logging with JSON output
- Fix eip7702_delegations_cleared detection logic

The fix changes from checking was_destroyed() to detecting
bytecode transition from EIP-7702 format to empty.

Add CLI configuration for slow block metrics:
- --debug.slow-block-threshold <duration> to set logging threshold
- Default: disabled (no slow block logging)
- Set to 0 to log all blocks

Add comprehensive tests for slow block metrics:
- EIP-7702 delegation set/cleared scenarios
- Contract deployment metrics
- Storage operation metrics
- Edge cases (revert, OOG)

Fix compilation errors from rebase onto upstream/main:
- Remove orphaned SlotStatus/inc_* merge remnants in cached_state.rs
- Add missing executor.finish() and db.merge_transitions() in payload_validator.rs
- Add account_cache_size field and get_cache_stats() method to CachedStateMetrics
- Add missing closing brace in metrics.rs record_block_execution
- Enable slow block logging in threshold filtering test
- Update verification report with post-rebase test results

…on report

Add 5 new tests to execution_metrics_test.rs for complete coverage of
slow_block_test_vectors.json:

- test_transfer_to_new_account_creates_account (A2)
- test_factory_deploys_multiple_contracts (C2)
- test_empty_block_metrics (EDGE1)
- test_reverted_transaction_excludes_state_changes (EDGE2)
- test_out_of_gas_reverts_all_changes (EDGE3)

- Add `const` to `timing_stats` function in ExecutedBlock
- Fix tab-to-space indentation in crates/evm/evm/Cargo.toml std features