feat: add gas/s and tx/s throughput metrics to invariant test output

[danieljrc888]

Summary

• Add throughput metrics (gas/s, tx/s) to invariant test output for benchmarking tools like scfuzzbench
• Track cumulative gas and elapsed time during invariant campaigns
• Add gas field to InvariantMetrics for per-selector gas tracking in the metrics table
• Extend inline JSON progress logging with total_txs, total_gas, tx_per_sec, gas_per_sec
• Display gas/s and tx/s in the human-readable test report line
• Update snapshot parsing regex to handle new format

Example output

Ran 2 tests for test/Vault.invariant.t.sol:VaultInvariantTest
[PASS] invariant_depositWithdrawAccounting() (runs: 20, calls: 2000, reverts: 0, gas/s: 1054698686, tx/s: 15399)

╭--------------+----------+-------+---------+----------+----------╮
| Contract     | Selector | Calls | Reverts | Discards | Gas      |
+=================================================================+
| VaultHandler | deposit  | 1041  | 0       | 0        | 65616418 |
|--------------+----------+-------+---------+----------+----------|
| VaultHandler | withdraw | 959   | 0       | 0        | 71370771 |
╰--------------+----------+-------+---------+----------+----------╯

[PASS] invariant_solvency() (runs: 20, calls: 2000, reverts: 0, gas/s: 1171893077, tx/s: 17092)

╭--------------+----------+-------+---------+----------+----------╮
| Contract     | Selector | Calls | Reverts | Discards | Gas      |
+=================================================================+
| VaultHandler | deposit  | 1041  | 0       | 0        | 65559742 |
|--------------+----------+-------+---------+----------+----------|
| VaultHandler | withdraw | 959   | 0       | 0        | 71566351 |
╰--------------+----------+-------+---------+----------+----------╯

Suite result: ok. 2 passed; 0 failed; 0 skipped; finished in 140.49ms (265.67ms CPU time)

Closes #13575

Test plan

• Unit tests for TestKindReport::Invariant display (normal, zero elapsed, optimization mode, failed corpus replays)
• Unit test for metrics table with Gas column
• Snapshot parsing tests updated for new format
• Integration test snapshots updated across all invariant test files
• cargo build -p forge passes
• cargo test -p forge --lib passes (36 tests)