fix(highlight): blend underline check and use struct key for attr cache

Problem: hl_blend_attrs() through-blend path only checked HL_UNDERLINE | HL_UNDERCURL
for sp_color blending, missing underdotted, combine/blend attr cache used (a << 16) + b
as map key which could overflow if attr IDs ever exceed 16 bits.

Solution: Use HL_UNDERLINE_MASK in the through-blend path to match all underline
styles. Use uint64_t with (a << 32) | b as map key via HlAttrKey macro so each
attr ID gets its full 32-bit range. Use HLATTRS_INIT in hl_get_underline() to
avoid duplicating default field values.

0 files changed, 0 insertions, 0 deletions