Feature: Configurable fsync for records and ledger writes

[evntd-jake]

While performance testing binary serialization, I hit an issue because I use an SSD that uses QLC for cheap high density storage. A smaller portion is used as an SLC write cache. See details on this LinkedIn post.

This change allows the consumer to trade durability for throughput.

The following will disable fsync on after event record and ledger writes.

mix fact.create --path tmp/nondurable \ 
  --record-file-writer-options sync=false \
  --ledger-file-writer-options sync=false

[evntd-jake]

Not sure if I really want to be releasing this. I'm leaning towards not, and instead creating a WAL to ensure the system is durable and crash proof in v0.3.0