RCA on #22945 [Bug]: Layer 1 fees has disappeared from the gas section for Optimism

### What is this about?

Performing a root-cause analysis of [this bug](https://github.com/MetaMask/metamask-extension/issues/22945) as part of [this epic](https://github.com/MetaMask/MetaMask-planning/issues/2103).

Data gathered and investigation results will be added in this ticket.

### Scenario

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### Design

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### Technical Details

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### Threat Modeling Framework

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### Acceptance Criteria

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### Stakeholder review needed before the work gets merged

- [ ] Engineering (needed in most cases)
- [ ] Design
- [ ] Product
- [ ] QA (automation tests are required to pass before merging PRs but not all changes are covered by automation tests - please review if QA is needed beyond automation tests)
- [ ] Security
- [ ] Legal
- [ ] Marketing
- [ ] Management (please specify)
- [ ] Other (please specify)

### References

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Start by reading the linked bug #22945 and the parent epic #2103 to understand the missing Layer 1 fee in Optimism's gas section. Investigate the reported behavior and add the root-cause findings and investigation results to this ticket; the issue provides no files, tests, or acceptance criteria.

Written by the indexing model from the issue text.