Fix use of absolute tolerance for iterative solvers

Issue/feature addressed

Currently, the option for using absolute tolerance is only properly implemented for static condensation.

Proposed solution

Generalize the implementation when using full iterative solver

Implementation

Tests

Suggested reviewers

Please suggest any people who would be appropriate to review your code.

Notes

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Checklist

• [ ] Functions and classes, or changes to them, are documented.
• [ ] User guide/documentation is updated.
• Changelog is updated.
• Suitable tests added for new functionality.
• Contributed code is correctly formatted. (See the contributing guidelines).
• [ ] License added to any new files.
• No extraneous files have been added (e.g. compiler output or test data files).