Force type specialization of ESDIRK*L2SA tableau dispatches

[singhharsh1708]

The _pure_esdirk_to_imex_tableau helper took stage count as runtime Int from size(Ai_mat, 1); now takes ::Val{S} so dispatch infers ESDIRKIMEXTableau{S, T, T2, :standard} concretely.

Checklist

• Appropriate tests were added
• Any code changes were done in a way that does not break public API
• All documentation related to code changes were updated
• The new code follows the
  contributor guidelines, in particular the SciML Style Guide and
  COLPRAC.
• Any new documentation only uses public API

Additional context

Add any other context about the problem here.

[singhharsh1708]

@ChrisRackauckas Re: your review on #3651 about type specialization of the ESDIRKIMEXTableau(::Alg, T, T2) dispatches — turned out 5 of them (the ESDIRK*L2SA family) were inferring as abstract ESDIRKIMEXTableau{_A, …} where _A because _pure_esdirk_to_imex_tableau was reading stage count as a runtime Int from size(Ai_mat, 1). Fixed by making the helper take ::Val{S} and passing Val(s) from each caller (they already had s = N as a local literal). All 23 dispatches now inline to concrete ESDIRKIMEXTableau{S, T, T2, E}. SDIRK convergence + DAE suites still pass.