KernelICA 2.0.0

Package reinstatement

This release reinstates KernelICA on CRAN after the package was previously archived.
The issues that led to the archival have been resolved, and the package has been updated to comply with current CRAN policies and checks.
Package maintenance has been transferred to a new maintainer.
Updated package metadata to reflect the current authorship and maintainer information.

Fixed an argument-order bug in the Hermite kernel implementation affecting kernel_matrix(..., kernel = "hermite") and incomplete_cholesky(..., kernel = "hermite").
Fixed validation of user-supplied initialization matrices in kernel_ica().
Fixed selection of the best solution across multiple random starts in kernel_ica().
Improved handling of empty vectors and zero-length loops in several functions by replacing 1:n and 1:length(x) with seq_len() and seq_along().
Added a guard in MD_distant_matrices() for cases where no additional matrices need to be generated.
incomplete_cholesky() now accepts integer input consistently by coercing input to numeric.
kernel_matrix() now validates the kernel argument using match.arg().
Corrected the sign in the exponent of the Gaussian kernel.

Modernized the C++ implementation by replacing manual memory management with std::unique_ptr.
Added missing standard library includes required by current compilers.
Added -DNDEBUG to release compilation flags.
Explicitly specified the package name when loading Rcpp modules.

Updated package documentation to derive author and maintainer information directly from DESCRIPTION.
Removed redundant author annotations from individual help pages.
Corrected the citation year for the kernel ICA reference.
Fixed several typographical errors in the documentation.