[Typescript-eslint] Fix `@typescript-eslint/restrict-plus-operands`

### What is this about?

Fix all errors with `// eslint-disable-next-line @typescript-eslint/restrict-plus-operands`
Reference: https://typescript-eslint.io/rules/restrict-plus-operands/

### 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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Search the repository for `eslint-disable-next-line @typescript-eslint/restrict-plus-operands` and review the affected files and nearby expressions. Read the linked `restrict-plus-operands` rule documentation before deciding how each error should be addressed. Done means the affected errors are fixed and the suppressions are no longer needed.

Written by the indexing model from the issue text.