remove thiserror

Gustav Sörnäsrequested to merge
thiserror into main

this mr removes the final usages of thiserror (except for in simulation-ext)

Author checklist

  • New Diagnostics have at least one snapshot test that triggers it
  • Added a changelog entry, if relevant
    • You can use ./add_changelog <MR number or a_descriptive_name> to do this

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