Rename stochastic_ld_sample to sketch_samples in RSS interfaces

[hsun3163]

Summary

This PR updates the RSS sketch-LD interface to use sketch_samples instead of stochastic_ld_sample, aligning pecotmr with
the current susieR::susie_rss() API.

It also fixes one sketch-LD loading bug: U_MIN / U_MAX from PLINK2 .afreq files were being read but dropped before
genotype rescaling, so the exact sketch inversion path could not run.

Motivation

There were two related issues:

1. Interface mismatch:

• pecotmr used stochastic_ld_sample
• current susieR uses sketch_samples

2. Sketch genotype restoration bug:

• read_afreq() correctly reads U_MIN / U_MAX
• but load_plink2_data() only merged id, alt_freq, and obs_ct
• so u_min / u_max were discarded before stochastic genotype inversion
• as a result, sketch genotype loading fell back to the warning path instead of restoring the original scale

Changes

API rename

• rename stochastic_ld_sample to sketch_samples in:
  • susie_rss_wrapper()
  • susie_rss_pipeline()
  • rss_analysis_pipeline()
• update internal forwarding to pass sketch_samples
• regenerate the related .Rd files

Sketch LD loading fix

In load_plink2_data():

• preserve u_min and u_max from .afreq when merging allele-frequency metadata into variant_info

variant_info <- merge(variant_info, afreq[, c("id", "alt_freq", "obs_ct")],
by = "id", all.x = TRUE, sort = FALSE)

After:

afreq_cols <- intersect(c("id", "alt_freq", "obs_ct", "u_min", "u_max"), colnames(afreq))
variant_info <- merge(variant_info, afreq[, afreq_cols, drop = FALSE],
by = "id", all.x = TRUE, sort = FALSE)

Why this matters:

• downstream code already checks for u_min / u_max
• without carrying those columns forward, the exact inversion branch is unreachable
• with this fix, stochastic sketch genotypes can be restored from min-max scaled PLINK2 storage as intended

Impact

• no intended methodological change
• interface naming is now consistent with susieR
• sketch-LD inversion now uses U_MIN / U_MAX when available, instead of unnecessarily falling back

Notes

This PR combines:

• an API-alignment change (stochastic_ld_sample -> sketch_samples)
• a small bug fix in sketch genotype restoration