Add mehod to go from SNP-level (SNPObject) to window-level ancestry information (LocalAncestryObject)

[miriambt]

Implemented the convert_to_window_level method within the SNPObject class to aggregate ancestry data into genomic windows within a LocalAncestryObject. This method supports three flexible options for defining windows:

1. Fixed Window Size:
   Specify a uniform size using window_size. The last window on each chromosome may be larger if SNPs are not evenly divisible by the size.

2. Custom Start and End Positions:
   Define windows with physical_pos (a 2D array of [start, end] base-pair coordinates).

   • If chromosomes is not provided and the dataset has only one chromosome, all windows are assumed to belong to that chromosome.
   • If multiple chromosomes exist but chromosomes is missing, an error will be raised.
   • Optionally, specify window_sizes to store the SNP count per window.

3. Matching Existing Windows:
   Reuse window definitions (physical_pos, chromosomes, window_sizes) from an existing laiobj.