feat: allow configuring clear-cache statically and injecting torn writes at runtime

[mj-ramos]

API update:

• allow configuring clear-cache as part of the static config
• allow injecting torn writes (torn-op and torn-seq) through the FIFO

[devzizu]

A couple of suggestions here before diving deep into a review:

1. If we want to add a type="clear" fault, then we must maintain the already known syntax, which is type=clear-cache, which indicates that specifying crash=false (assume default) has the same effect has sending lazyfs::clear-cache to the faults fifo.

   • With this new type, and the option to specify crash=true, we must remove lazyfs::crash from the API and replace by lazyfs::clear-cache with more options, namely the timing, op, occurrence, and crash (e.g., lazyfs::clear-cache::timing=...::op=...::occurrence=...::crash), where crash may be omitted (optional parameter).
   • We must also ensure the user never pre-configures a clear-cache without a timing and op, but he can send lazyfs::clear-cache::crash to the fifo to simulate "crash right now".

2. Instead of the above, why can't we just add support for the existing lazyfs::crash fault under the config file? Do we need to specify a timing for the clear cache without crashing LazyFS?

WDYT?

[devzizu]

TL;DR: We going with option 1, but maintaining the crash fault option for now and will probably deprecate it soon. @mj-ramos Can you please change the fault syntax of the clear fault type to clear-cache?

[devzizu]

We'll leave some of the suggestions for later improvements.