`read_ld()` Read ld from either internal or external file.
read_ld(ld)A data frame (tibble) containing LD score information read from the specified directory. Each row corresponds to a SNP, and columns typically include:
CHR: Chromosome number.
SNP: SNP identifier (rsID).
BP: Base pair position.
L2: LD score value.
M: Number of SNPs used in the LD score computation.
(character) Path to directory containing ld score files, ending in `*.l2.ldscore.gz`. Default is `NA`, which will utilize the built-in ld score files from Pan-UK Biobank for the ancestry specified in `ancestry`.