Fix R CMD check on Windows: propagate .libPaths() to PSOCK eFDR workers

[ZoliQua]

Problem

set_based_enrichment_test() runs the resampling eFDR on a PSOCK cluster and loads the package on
each worker with clusterEvalQ(cl, library("mulea")). PSOCK workers are fresh R sessions that do
not inherit the parent's .libPaths(). When mulea is not on a worker's default library tree —
most notably the temporary *.Rcheck library used during R CMD check — library("mulea") fails
on the workers and the whole call aborts.

In practice this breaks R CMD check on Windows, where re-building the vignette (mulea.Rmd,
which runs eFDR with nthreads = 2) fails with:

--- re-building 'mulea.Rmd' using rmarkdown
Error in checkForRemoteErrors(...) :
  2 nodes produced errors; first error: there is no package called 'mulea'
--- failed re-building 'mulea.Rmd'
Error: Vignette re-building failed.

Unix workers happen to pick up the check library via the inherited R_LIBS environment, so the
failure is Windows-specific, but the underlying cluster setup is fragile on every platform.

Fix

Capture the host's library paths, export them to the workers, and set them before loading the
package:

worker_libpaths <- .libPaths()
clusterExport(cl, c(..., "worker_libpaths"), envir = environment())
clusterEvalQ(cl, { .libPaths(worker_libpaths); library("mulea") })

One file changed (R/set-based-enrichment-test.r), plus a NEWS.md entry and a patch version bump.

Why it is safe

The change only affects how the workers locate the package. It does not touch the RNG, the
per-thread seeding (seeds_per_thread), the C++ simulation, or any arithmetic, so eFDR results are
unchanged. In normal installed use the workers already resolve library("mulea") via the default
library path, so this is purely a check/build-robustness fix with no behavioural change for users.

Verification

• On an installed build, ora(..., p_value_adjustment_method = "eFDR", nthreads = 2) runs without
  error and its p_value column is byte-identical to the serial (nthreads = 1) path.
• The full R-CMD-check matrix now passes on windows-latest (previously failing on the vignette
  rebuild), alongside ubuntu-latest release/devel and macOS.