Add crash tests

[harshil-goel]

Crash after shadow reaches boundary, before descriptor append
Crash after descriptor fsync, before commit enters worker queue
Crash after commit queues, before ClickHouse DDL begins
Crash after first ClickHouse ALTER statement, before remaining statements
Crash after complete ClickHouse DDL, before emitter acknowledgment
Crash after in-memory acknowledgment, before manifest fsync
Crash after manifest fsync, before descriptor GC