Possibly implement longer-term predictions given by IERS A #14811

What is the problem this feature will solve?

From #14756 (comment):

i noticed that in in the Bulletin A there are equations provided to extend predictions beyond the end of the table: https://datacenter.iers.org/data/latestVersion/bulletinA.txt. might be worth considering implementing those as a fallback if the IERS data doesn't extend far enough for a calculation. would add the overhead of periodically updating the coefficients, though, so perhaps not the trouble.

Describe the desired outcome

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Additional context

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