fix: use na_rep instead of string 'None' for missing score and count data in CSV export#661

bencap wants to merge 2 commits intorelease-2026.1.1VariantEffect/mavedb-api:release-2026.1.1from

bugfix/bencap/636/na-rep-not-applying-to-scores-or-countsVariantEffect/mavedb-api:bugfix/bencap/636/na-rep-not-applying-to-scores-or-countsCopy head branch name to clipboard