Lanczos exponential: allocate batches as needed
Description
This removes the need of specifying TDExpOrder as the batches are allocated to the order needed, with 200 as the maximum order. This makes it much more user-friendly.
News snippet
Lanczos exponential uses automatic order, TDExpOrder not needed anymore
Checklist
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I have checked that my code follows the Octopus coding standards -
I have added tests for all the new features added in this request.