cannon,op-challenger: Add metric to report i-cache misses

[Inphi]

The instruction pre-heap contains a cache of decoded instructions. It is initialized the first time Cannon is executed using a 2 GiB region. In almost all cases, this is sufficient to cover all instructions in a program. In rare cases, such as when the program exceeds 2 GiB or due to misconfiguration, a cache miss may occur. Detecting this today is not straightforward.

This patch adds a metric to track cache misses in the pre-heap, making it easier to identify when they happen.

[codecov]

Codecov Report

❌ Patch coverage is 53.33333% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 45.39%. Comparing base (2da6ec7) to head (e90e569).
⚠️ Report is 4 commits behind head on develop.

Files with missing lines	Patch %	Lines
cannon/mipsevm/multithreaded/stats.go	37.50%	5 Missing ⚠️
op-challenger/metrics/vm.go	60.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #17123      +/-   ##
===========================================
+ Coverage    43.74%   45.39%   +1.64%     
===========================================
  Files         1372     1478     +106     
  Lines       115501   120096    +4595     
===========================================
+ Hits         50524    54514    +3990     
- Misses       61134    61758     +624     
+ Partials      3843     3824      -19     

Flag	Coverage Δ
cannon-go-tests-64	65.95% <44.44%> (-0.05%)	⬇️
contracts-bedrock-tests	96.28% <ø> (?)

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

Files with missing lines	Coverage Δ
cannon/mipsevm/multithreaded/mips.go	91.66% <100.00%> (+0.02%)	⬆️
op-challenger/game/fault/trace/vm/executor.go	61.01% <100.00%> (+0.33%)	⬆️
op-challenger/metrics/vm.go	32.40% <60.00%> (+1.33%)	⬆️
cannon/mipsevm/multithreaded/stats.go	84.12% <37.50%> (-6.79%)	⬇️

... and 122 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.

[ajsutton]

LGTM.