BUG: Fix num. time steps for iterative models and in progress bar

Proposed changes

Inconsistency in time step numbers in:

Iterative models. Now the check-if-final-time is reached is done by calling the method final_time_reached()
Progress bar: A rounding error caused visualization of the wrong final time step number. This is fixed by using np.round(), which rounds e.g. the time 199.999999 to 200 instead of rounding down to 199, as the int()-functionality did before.

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[ ] Minor change (e.g., dependency bumps, broken links).
[x] Bugfix (non-breaking change which fixes an issue).
[ ] New feature (non-breaking change which adds functionality).
[ ] Breaking change (fix or feature that would cause existing functionality to not work as expected).
[ ] Testing (contribution related to testing of existing or new functionality).
[ ] Documentation (contribution related to adding, improving, or fixing documentation).
[ ] Maintenance (e.g., improve logic and performance, remove obsolete code).
[ ] Other:

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[x] The documentation is up-to-date.
[x] Static typing is included in the update.
[x] This PR does not duplicate existing functionality.
[ ] The update is covered by the test suite (including tests added in the PR).
[ ] If new skipped tests have been introduced in this PR, pytest was run with the --run-skipped flag.