vm-runner: Rework l2 block selection

[mbaxter]

Description

Rework vm-runner L2 block selection to better ensure we are using an L2 block that is safe with respect to the chosen L1 head.

[ajsutton]

LGTM.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (d4657b7) to head (623c70f).
⚠️ Report is 30 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff              @@
##           develop   #17089       +/-   ##
============================================
- Coverage    77.26%        0   -77.27%     
============================================
  Files          169        0      -169     
  Lines         9934        0     -9934     
============================================
- Hits          7676        0     -7676     
+ Misses        2099        0     -2099     
+ Partials       159        0      -159     

Flag	Coverage Δ
cannon-go-tests-64	?
contracts-bedrock-tests	?

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see 169 files with indirect coverage changes

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