GasPriceOracle: remove saturating math from getOperatorFee (jovian)

[geoknee]

This cherry picks #17913 (already merged to develop) onto the release branch for op-contracts/v5.0.0 so we can cut a new RC.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.15%. Comparing base (aeed703) to head (f6e2e48).
⚠️ Report is 2 commits behind head on proposal/op-contracts/v5.0.0.

Additional details and impacted files

@@                       Coverage Diff                        @@
##           proposal/op-contracts/v5.0.0   #17998      +/-   ##
================================================================
+ Coverage                         74.64%   81.15%   +6.51%     
================================================================
  Files                               174      119      -55     
  Lines                             11105     6320    -4785     
================================================================
- Hits                               8289     5129    -3160     
+ Misses                             2672     1191    -1481     
+ Partials                            144        0     -144     

Flag	Coverage Δ
cannon-go-tests-64	?
contracts-bedrock-tests	81.15% <100.00%> (ø)

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Files with missing lines	Coverage Δ
...ckages/contracts-bedrock/src/L2/GasPriceOracle.sol	100.00% <100.00%> (ø)

... and 55 files with indirect coverage changes

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