ref(crons): Add Fugit schedule conversion helper (#3141)

* ref(crons): Add Fugit schedule conversion helper

Add Sentry::Cron::FugitSchedule, which turns fugit cron lines and
intervals into monitor configs. It returns nil for schedules Sentry
would read differently. Shared by the rufus-scheduler and Solid Queue
integrations. fugit is added as a dev dependency for the specs.

Co-Authored-By: Claude <noreply@anthropic.com>

* feat(crons): Convert L, # and whole-hour offsets to Crons schedules

Co-Authored-By: Claude <noreply@anthropic.com>

* ref(crons): Shorten comments

Co-Authored-By: Claude <noreply@anthropic.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: wedamija

sentry-ruby/Gemfile

@@ -35,6 +35,7 @@ gem "webrick"
 gem "faraday"
 gem "excon"
 gem "webmock"
+gem "fugit"
 
 group :sequel do
   gem "sequel"