[isoltest] Formatting should support strings longer than 32 bytes

The following test
```
contract C {
function e() public {
revert("Transaction failed. Transaction failed.");
}
}
// ====
// EVMVersion: >homestead
// ----
// e() ->
```
does not handle strings longer than 32 bytes correctly:
```
// e() -> FAILURE, hex"08c379a0", 0x20, 39, "Transaction failed. Transaction "
```

Start with the supplied isoltest contract case and reproduce the output for the longer revert string. Trace the formatter that emits the FAILURE line and compare its handling of the 32-byte boundary with the expected value. Done means strings longer than 32 bytes are formatted correctly and the relevant isoltest coverage passes.

Written by the indexing model from the issue text.