FastSurvival 0.1.0

• Initial release.
• Core computations implemented in C++ via Rcpp for use inside large simulation loops.
• survfit_fast(): single-time-point Kaplan-Meier estimator with Greenwood standard error and plain / log / log-log confidence intervals. The C++ backend locates the evaluation cutoff via binary search and accumulates the Kaplan-Meier product and Greenwood variance sum in a single scan over event positions. Returns an object of class "survfit_fast" with a print() method.
• survdiff_fast(): log-rank test returning a one-sided Z-score or a two-sided chi-square statistic. The C++ backend uses a two-pointer merge scan over pooled sorted vectors, eliminating the rank construction, tabulate(), and reverse cumulative sum operations of the standard implementation. Returns an object of class "survdiff_fast" with a print() method.
• coxph_fast(): closed-form hazard ratio estimator via the Pike-Halley Estimator method with Wald confidence interval. The C++ backend performs group splitting, at-risk counting, and per-distinct-event-time accumulation in a single pass. Returns an object of class "coxph_fast" with a print() method.
• simdata_fast(): clinical trial data simulator supporting one- and two-group designs, piecewise uniform accrual, and simple and piecewise exponential survival and dropout times. C++ backends handle piecewise sampling and two-group interleaving, and random number generation uses dqrng.