op-node: Search valid unsafe head backwards

[sebastianst]

Description

Changes the search for the latest valid unsafe head (valid per canonical L1 origin) in the supervisor-instructed reset to go backwards. L1 reorgs are usually shallow, and resets sometimes are for other reasons than an L1 reorg, so going backwards will almost always be a much quicker option.

Tests

Existing L1 reorg acceptance tests should still pass.

Additional context

The old forwards-search prevented some nodes on the rehearsal network from resetting in time. With backwards search, they got unstuck.

We will probably switch to a binary search with #16276

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.24%. Comparing base (158e990) to head (d81b2a1).
Report is 8 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff              @@
##           develop   #16312       +/-   ##
============================================
+ Coverage    46.67%   96.24%   +49.57%     
============================================
  Files         1368      106     -1262     
  Lines       110795     4583   -106212     
============================================
- Hits         51714     4411    -47303     
+ Misses       55435      172    -55263     
+ Partials      3646        0     -3646     

Flag	Coverage Δ
cannon-go-tests-64	?
contracts-bedrock-tests	96.24% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

see 1262 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.