Update nSurv and gsSurv to support Schoenfeld method + test coverage improvements

[nanxstats]

Closes #194

This PR ports the work from the issue-194 branch (which was ported from the gsSurv Quarto book repo) to have a minimal diff. This mostly involves cherry-picking gsSurv/nSurv survival design updates and related method/docs updates + porting patched tests and new developer coverage tests.

• Updated nSurv() and gsSurv() to incorporate Schoenfeld and Freedman methods for sample size and power for time-to-event studies with proportional hazards. This allows matching versus other software.
• Corrected weighting for stratified time-to-event studies with proportional hazards. This was done for Lachin-Foulkes method, but we also added Bernstein and Lagakos method.
• Refreshed print.nSurv()/print.gsSurv() output formatting.
• Increased unit test coverage across core gsDesign, spending, and binomial utilities.
• Updated benchmark baseline .cywx files to match current outputs.

[keaven]

Need update to test.type text strings; I will do this.
3 = "Two-sided asymmetric with binding futility bound"
5 = "Two-sided asymmetric with binding harm bound"
6 = "Two-sided asymmetric with non-binding harm bound"