Fix PFASST I/O and pre-initialize coarse preconditioner for Parareal

Issue/feature addressed

For Parareal, the initialization of the preconditioner on the serial-in-time coarse solver cause significant overhead proportional to the number of time step. This MR also fixes an I/O bug with PFASST.

Proposed solution

Artificially run one step on the coarse solver to initialize the preconditioner for Parareal.

Implementation

Tests

Suggested reviewers

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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).