Add Biswas 2025 IMEX tableaus

[cwittens]

OpenClaw note

This PR was done by OpenClaw to see how well it can work autonomously. Collin will turn it into a real PR, not draft, if he has hand checked everything himself.

Summary

This draft PR adds the coefficient-only IMEX Runge-Kutta tableaus from Biswas, Ketcheson, Ranocha, and Schütz (2025) that were missing from Theseus/Ariadne:

• AGSA342 from Table 12
• KenCarpARK324L2SA / ARK3(2)4 L[2]SA from Table 16
• KenCarpARK436L2SA / ARK4(3)6 L[2]SA from Table 17

It also adds the methods to the Theseus docs and extends the IMEX convergence tests.

This addresses part of #124.

Notes

The coefficients were taken from the paper PDF appendix tables, not from external coefficient searches. The additions are intended to be low-risk coefficient-table additions only: no solver logic, Newton/Krylov behavior, adaptivity, or stepping machinery was changed.

Table 12 has one apparent labeling typo/repetition in the PDF coefficient paragraph, where ã32 appears twice. The second occurrence is interpreted as the implicit a32, consistent with the tableau layout.

Testing

Locally run with Julia 1.12.5:

julia --project=libs/Theseus -e 'using Pkg; Pkg.test()'

Result:

Overall: 63 passed, 4 broken, 67 total
SUCCESS

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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